diff --git a/include/globals.h b/include/globals.h
index 6f1b55ed..a3f3bbea 100644
--- a/include/globals.h
+++ b/include/globals.h
@@ -115,7 +115,6 @@ extern TaskHandle_t irqHandlerTask, ClockTask;
 extern TimerHandle_t WifiChanTimer;
 extern Timezone myTZ;
 extern time_t LastSyncTime;
-extern RtcDateTime compiled;
 
 // application includes
 #include "led.h"
diff --git a/include/timemanager.h b/include/timemanager.h
index dcc5ca87..16f828fa 100644
--- a/include/timemanager.h
+++ b/include/timemanager.h
@@ -13,14 +13,18 @@
 #include "dcf77.h"
 #endif
 
+time_t tmConvert_t(uint16_t YYYY, uint8_t MM, uint8_t DD, uint8_t hh,
+                   uint8_t mm, uint8_t ss);
 void clock_init(void);
 void clock_loop(void *pvParameters);
 void time_sync(void);
-bool wait_for_pulse(void);
+int wait_for_pulse(void);
 int syncTime(time_t);
 int syncTime(uint32_t t);
 void IRAM_ATTR CLOCKIRQ(void);
 int timepulse_init(void);
 void timepulse_start(void);
+int TimeIsValid(time_t t);
+time_t compiledUTC(void);
 
 #endif // _timemanager_H
\ No newline at end of file
diff --git a/src/cyclic.cpp b/src/cyclic.cpp
index 11ba7c5b..8393f2b9 100644
--- a/src/cyclic.cpp
+++ b/src/cyclic.cpp
@@ -7,7 +7,7 @@
 // Local logging tag
 static const char TAG[] = "main";
 
-time_t userUTCTime; // Seconds since the UTC epoch
+time_t userUTCTime; // Seconds since the UTC in seconds GPS time starting 1.1.2000
 
 // do all housekeeping
 void doHousekeeping() {
diff --git a/src/display.cpp b/src/display.cpp
index f4f6abe8..9c949e75 100644
--- a/src/display.cpp
+++ b/src/display.cpp
@@ -134,8 +134,7 @@ void init_display(const char *Productname, const char *Version) {
     u8x8.printf(!cfg.rssilimit ? "RLIM:off " : "RLIM:%d", cfg.rssilimit);
 
     I2C_MUTEX_UNLOCK(); // release i2c bus access
-  }
-
+  }                     // mutex
 } // init_display
 
 void refreshtheDisplay() {
@@ -155,8 +154,10 @@ void refreshtheDisplay() {
     }
 
     // if display is switched off we don't refresh it to relax cpu
-    if (!DisplayState)
+    if (!DisplayState) {
+      I2C_MUTEX_UNLOCK(); // release i2c bus access
       return;
+    }
 
     // update counter (lines 0-1)
     snprintf(
@@ -226,12 +227,11 @@ void refreshtheDisplay() {
     u8x8.printf("%-16s", display_line6);
 #else // we want a systime display instead LoRa status
     t = myTZ.toLocal(now());
-    timePulse = (timeStatus() == timeSet) ? timePulseSymbol : timeNoPulseSymbol;
-    timeState = TimePulseTick ? timeSync : ' ';
+    timePulse = TimeIsSynced ? timePulseSymbol : timeNoPulseSymbol;
+    timeState = TimePulseTick ? timePulse : ' ';
     TimePulseTick = false;
-    u8x8.printf("%02d:%02d%c%02d%c %2d.%3s", hour(t), minute(t),
-                TimeIsSynced ? ':' : '.', second(t), timeState, day(t),
-                printmonth[month(t)]);
+    u8x8.printf("%02d:%02d:%02d%c %2d.%3s", hour(t), minute(t), second(t),
+                timeState, day(t), printmonth[month(t)]);
 #endif
 
     // update LMiC event display (line 7)
@@ -250,8 +250,7 @@ void refreshtheDisplay() {
 #endif // HAS_LORA
 
     I2C_MUTEX_UNLOCK(); // release i2c bus access
-  }
-
+  }                     // mutex
 } // refreshDisplay()
 
 #endif // HAS_DISPLAY
\ No newline at end of file
diff --git a/src/gpsread.cpp b/src/gpsread.cpp
index d9b6d281..d8a397c2 100644
--- a/src/gpsread.cpp
+++ b/src/gpsread.cpp
@@ -73,19 +73,6 @@ void gps_read() {
            gps.passedChecksum(), gps.failedChecksum(), gps.sentencesWithFix());
 }
 
-// helper function to convert gps date/time into time_t
-time_t tmConvert_t(uint16_t YYYY, uint8_t MM, uint8_t DD, uint8_t hh,
-                   uint8_t mm, uint8_t ss) {
-  tmElements_t tm;
-  tm.Year = YYYY - 1970; // note year argument is offset from 1970 in time.h
-  tm.Month = MM;
-  tm.Day = DD;
-  tm.Hour = hh;
-  tm.Minute = mm;
-  tm.Second = ss;
-  return makeTime(tm);
-}
-
 // function to fetch current time from gps
 time_t get_gpstime(void) {
   // !! never call now() or delay in this function, this would break this
@@ -93,8 +80,10 @@ time_t get_gpstime(void) {
 
   time_t t = 0;
 
-  if ((gps.time.age() < 900) && (gps.time.isValid()) &&
-      (gps.date.year() >= compiled.Year())) {
+  if ((gps.time.age() < 950) && (gps.time.isValid())) {
+
+    ESP_LOGD(TAG, "GPS time age: %dms, is valid: %s", gps.time.age(),
+             gps.time.isValid() ? "yes" : "no");
 
     // use recent gps time
     t = tmConvert_t(gps.date.year(), gps.date.month(), gps.date.day(),
diff --git a/src/lmic_config.h b/src/lmic_config.h
index eb9b53c7..50c0b4ad 100644
--- a/src/lmic_config.h
+++ b/src/lmic_config.h
@@ -22,7 +22,7 @@
 //#define LMIC_USE_INTERRUPTS
 
 //time sync via LoRaWAN network, is not yet supported by TTN (LoRaWAN spec v1.0.3)
-//#define LMIC_ENABLE_DeviceTimeReq 1
+#define LMIC_ENABLE_DeviceTimeReq 1
 
 // 16 μs per tick
 // LMIC requires ticks to be 15.5μs - 100 μs long
diff --git a/src/lorawan.cpp b/src/lorawan.cpp
index 789cf92b..f94c60d0 100644
--- a/src/lorawan.cpp
+++ b/src/lorawan.cpp
@@ -459,7 +459,8 @@ void user_request_network_time_callback(void *pVoidUserUTCTime,
   }
 
   // Update userUTCTime, considering the difference between the GPS and UTC
-  // epoch, and the leap seconds
+  // time, and the leap seconds
+  // !!! DANGER !!! This code will expire in the year when next leap second happenes
   *pUserUTCTime = lmicTimeReference.tNetwork + 315964800;
   // Current time, in ticks
   ostime_t ticksNow = os_getTime();
@@ -474,7 +475,7 @@ void user_request_network_time_callback(void *pVoidUserUTCTime,
   if (syncTime(*pUserUTCTime)) { // do we have a valid time?
 #ifdef HAS_RTC
     if (TimeIsSynced)
-      set_rtctime(now()); // epoch time
+      set_rtctime(now()); // UTC time
 #endif
     LastSyncTime = now(); // remember time of this sync event
     ESP_LOGI(TAG, "LORA has set the system time");
diff --git a/src/main.cpp b/src/main.cpp
index 6f02cfd6..4211de6e 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -65,7 +65,8 @@ uint8_t volatile channel = 0;              // channel rotation counter
 uint16_t volatile macs_total = 0, macs_wifi = 0, macs_ble = 0,
                   batt_voltage = 0; // globals for display
 
-hw_timer_t *sendCycle = NULL, *homeCycle = NULL, *clockCycle = NULL, *displaytimer = NULL;
+hw_timer_t *sendCycle = NULL, *homeCycle = NULL, *clockCycle = NULL,
+           *displaytimer = NULL;
 
 TaskHandle_t irqHandlerTask, ClockTask;
 SemaphoreHandle_t I2Caccess, TimePulse;
@@ -73,8 +74,6 @@ bool volatile TimePulseTick = false;
 bool TimeIsSynced = false;
 time_t LastSyncTime = 0;
 
-RtcDateTime compiled = RtcDateTime(__DATE__, __TIME__);
-
 // container holding unique MAC address hashes with Memory Alloctor using PSRAM,
 // if present
 std::set<uint16_t, std::less<uint16_t>, Mallocator<uint16_t>> macs;
@@ -82,7 +81,7 @@ std::set<uint16_t, std::less<uint16_t>, Mallocator<uint16_t>> macs;
 // initialize payload encoder
 PayloadConvert payload(PAYLOAD_BUFFER_SIZE);
 
-// set Time Zone, fetch user setting from paxcounter.conf
+// set Time Zone for user setting from paxcounter.conf
 TimeChangeRule myDST = DAYLIGHT_TIME;
 TimeChangeRule mySTD = STANDARD_TIME;
 Timezone myTZ(myDST, mySTD);
@@ -97,7 +96,7 @@ void setup() {
 
   char features[100] = "";
 
-  // create some semaphores for syncing / mutexing tasks
+    // create some semaphores for syncing / mutexing tasks
   I2Caccess = xSemaphoreCreateMutex(); // for access management of i2c bus
   if (I2Caccess)
     xSemaphoreGive(I2Caccess); // Flag the i2c bus available for use
diff --git a/src/rtctime.cpp b/src/rtctime.cpp
index 7f39b361..a3bf3fcf 100644
--- a/src/rtctime.cpp
+++ b/src/rtctime.cpp
@@ -10,63 +10,52 @@ RtcDS3231<TwoWire> Rtc(Wire); // RTC hardware i2c interface
 // initialize RTC
 int rtc_init(void) {
 
-  // return = 0 -> error / return = 1 -> success
-
-  // block i2c bus access
-  if (I2C_MUTEX_LOCK()) {
+  if (I2C_MUTEX_LOCK()) { // block i2c bus access
 
     Wire.begin(HAS_RTC);
     Rtc.Begin();
 
-    if (!Rtc.IsDateTimeValid()) {
-      ESP_LOGW(TAG,
-               "RTC has no valid RTC date/time, setting to compilation date");
-      Rtc.SetDateTime(compiled);
-    }
+    // configure RTC chip
+    Rtc.Enable32kHzPin(false);
+    Rtc.SetSquareWavePin(DS3231SquareWavePin_ModeNone);
 
     if (!Rtc.GetIsRunning()) {
       ESP_LOGI(TAG, "RTC not running, starting now");
       Rtc.SetIsRunning(true);
     }
 
-    RtcDateTime now = Rtc.GetDateTime();
+    RtcDateTime tt = Rtc.GetDateTime();
+    time_t t = tt.Epoch32Time(); // sec2000 -> epoch
 
-    if (now < compiled) {
-      ESP_LOGI(TAG, "RTC date/time is older than compilation date, updating");
-      Rtc.SetDateTime(compiled);
+    if (!Rtc.IsDateTimeValid() || !TimeIsValid(t)) {
+      ESP_LOGW(TAG, "RTC has no recent time, setting to compilation date");
+      Rtc.SetDateTime(
+          RtcDateTime(compiledUTC() - SECS_YR_2000)); // epoch -> sec2000
     }
 
-    // configure RTC chip
-    Rtc.Enable32kHzPin(false);
-    Rtc.SetSquareWavePin(DS3231SquareWavePin_ModeNone);
-
+    I2C_MUTEX_UNLOCK(); // release i2c bus access
+    ESP_LOGI(TAG, "RTC initialized");
+    return 1; // success
   } else {
-    ESP_LOGE(TAG, "I2c bus busy - RTC initialization error");
-    goto error;
+    ESP_LOGE(TAG, "RTC initialization error, I2C bus busy");
+    return 0; // failure
   }
 
-  I2C_MUTEX_UNLOCK(); // release i2c bus access
-  ESP_LOGI(TAG, "RTC initialized");
-  return 1;
-
-error:
-  I2C_MUTEX_UNLOCK(); // release i2c bus access
-  return 0;
-
 } // rtc_init()
 
-int set_rtctime(time_t t) { // t is seconds epoch time starting 1.1.1970
+int set_rtctime(time_t t) { // t is UTC in seconds epoch time
   if (I2C_MUTEX_LOCK()) {
-    Rtc.SetDateTime(RtcDateTime(t));
-    I2C_MUTEX_UNLOCK(); // release i2c bus access
+    Rtc.SetDateTime(RtcDateTime(t - SECS_YR_2000)); // epoch -> sec2000
+    I2C_MUTEX_UNLOCK();
     ESP_LOGI(TAG, "RTC time synced");
     return 1; // success
-  }
-  ESP_LOGE(TAG, "RTC set time failure");
-  return 0; // failure
+  } else {
+    ESP_LOGE(TAG, "RTC set time failure");
+    return 0;
+  } // failure
 } // set_rtctime()
 
-int set_rtctime(uint32_t t) { // t is epoch seconds starting 1.1.1970
+int set_rtctime(uint32_t t) { // t is UTC in seconds epoch time
   return set_rtctime(static_cast<time_t>(t));
   // set_rtctime()
 }
@@ -74,25 +63,23 @@ int set_rtctime(uint32_t t) { // t is epoch seconds starting 1.1.1970
 time_t get_rtctime(void) {
   // !! never call now() or delay in this function, this would break this
   // function to be used as SyncProvider for Time.h
-  time_t t = 0; // 0 effects calling SyncProvider() to not set time
-  // block i2c bus access
+  time_t t = 0;
   if (I2C_MUTEX_LOCK()) {
     if (Rtc.IsDateTimeValid() && Rtc.GetIsRunning()) {
       RtcDateTime tt = Rtc.GetDateTime();
-      t = tt.Epoch32Time();
+      t = tt.Epoch32Time(); // sec2000 -> epoch
     }
-    I2C_MUTEX_UNLOCK(); // release i2c bus access
+    I2C_MUTEX_UNLOCK();
   }
   return t;
 } // get_rtctime()
 
 float get_rtctemp(void) {
-  // block i2c bus access
   if (I2C_MUTEX_LOCK()) {
     RtcTemperature temp = Rtc.GetTemperature();
-    I2C_MUTEX_UNLOCK(); // release i2c bus access
+    I2C_MUTEX_UNLOCK();
     return temp.AsFloatDegC();
-  } // while
+  }
   return 0;
 } // get_rtctemp()
 
diff --git a/src/timemanager.cpp b/src/timemanager.cpp
index 9adac15d..ee24c2c2 100644
--- a/src/timemanager.cpp
+++ b/src/timemanager.cpp
@@ -5,7 +5,7 @@ static const char TAG[] = "main";
 
 void time_sync() {
   // synchonization of systime with external time source (GPS/LORA)
-  // function is frequently called from cyclic.cpp
+  // frequently called from cyclic.cpp
 
 #ifdef TIME_SYNC_INTERVAL
 
@@ -25,12 +25,11 @@ void time_sync() {
 #ifdef HAS_RTC
   if (TimeIsSynced) { // recalibrate RTC, if we have one
     set_rtctime(now());
-  } 
-  else { // we switch to fallback time after a while
+  } else { // we switch to fallback time after a while
     if ((lastTimeSync >= (TIME_SYNC_TIMEOUT * 60000)) ||
-        !LastSyncTime) {       // sync stil due -> use RTC as fallback source
+        !LastSyncTime) { // sync is still due -> use RTC as fallback source
       syncTime(get_rtctime()); // sync with RTC time
-      TimeIsSynced = false;    // 
+      TimeIsSynced = false;
     }
   }
 #endif
@@ -40,33 +39,33 @@ void time_sync() {
 
 // helper function to sync time on start of next second
 int syncTime(time_t t) {
-  if (t) {
+  if (TimeIsValid(t)) {
     TimeIsSynced = wait_for_pulse(); // wait for next 1pps timepulse
     setTime(t);
     adjustTime(1);        // forward time to next second
     LastSyncTime = now(); // store time of this sync
-    ESP_LOGD(TAG, "System time was set to %02d:%02d:%02d", hour(t), minute(t),
+    ESP_LOGD(TAG, "Time was set to %02d:%02d:%02d", hour(t), minute(t),
              second(t));
     return 1; // success
   } else {
-    ESP_LOGD(TAG, "System time sync attempt failed");
+    ESP_LOGD(TAG, "Time sync attempt failed");
     TimeIsSynced = false;
     return 0;
   }
   // failure
 }
 
-int syncTime(uint32_t t) { // t is epoch seconds starting 1.1.1970
+int syncTime(uint32_t t) { // t is UTC time in seconds epoch
   return syncTime(static_cast<time_t>(t));
 }
 
 // helper function to sync moment on timepulse
-bool wait_for_pulse(void) {
+int wait_for_pulse(void) {
   // sync on top of next second with 1pps timepulse
   if (xSemaphoreTake(TimePulse, pdMS_TO_TICKS(1000)) == pdTRUE)
-    return true; // success
+    return 1; // success
   ESP_LOGD(TAG, "Missing timepulse");
-  return false;
+  return 0; // failure
 }
 
 // helper function to setup a pulse per second for time synchronisation
@@ -95,7 +94,7 @@ int timepulse_init() {
     ESP_LOGI(TAG, "Timepulse: external (RTC)");
     return 1; // success
   } else {
-    ESP_LOGE(TAG, "I2c bus busy - RTC initialization error");
+    ESP_LOGE(TAG, "RTC initialization error, I2C bus busy");
     return 0; // failure
   }
   return 1; // success
@@ -132,6 +131,34 @@ void IRAM_ATTR CLOCKIRQ(void) {
   portYIELD_FROM_ISR();
 }
 
+// helper function to check plausibility of a time
+int TimeIsValid(time_t t) {
+  // is it a time in the past? we use compile date to guess
+  ESP_LOGD(TAG, "t=%d, tt=%d, valid: %s", t, compiledUTC(),
+           (t >= compiledUTC()) ? "yes" : "no");
+  return (t >= compiledUTC());
+}
+
+// helper function to convert compile time to UTC time
+time_t compiledUTC(void) {
+  time_t t = RtcDateTime(__DATE__, __TIME__).Epoch32Time();
+  return myTZ.toUTC(t);
+}
+
+// helper function to convert gps date/time into time_t
+time_t tmConvert_t(uint16_t YYYY, uint8_t MM, uint8_t DD, uint8_t hh,
+                   uint8_t mm, uint8_t ss) {
+  tmElements_t tm;
+  tm.Year =
+      CalendarYrToTm(YYYY); // year offset from 1970 in time.h
+  tm.Month = MM;
+  tm.Day = DD;
+  tm.Hour = hh;
+  tm.Minute = mm;
+  tm.Second = ss;
+  return makeTime(tm);
+}
+
 #if defined HAS_IF482 || defined HAS_DCF77
 
 #if defined HAS_DCF77 && defined HAS_IF482