diff --git a/scripts/getVersion.py b/scripts/getVersion.py
index ffcc2714..f7c825ce 100644
--- a/scripts/getVersion.py
+++ b/scripts/getVersion.py
@@ -56,19 +56,16 @@ def readVersion(path, infile):
     src = path + ".pio/build/esp8266-release/firmware.bin"
     dst = path + "firmware/" + versionout
     os.rename(src, dst)
-    gzip_bin(dst, dst + ".gz")
 
     versionout = version[:-1] + "_esp8266_nokia5110_" + sha + ".bin"
     src = path + ".pio/build/esp8266-nokia5110/firmware.bin"
     dst = path + "firmware/" + versionout
     os.rename(src, dst)
-    gzip_bin(dst, dst + ".gz")
 
     versionout = version[:-1] + "_esp8266_ssd1306_" + sha + ".bin"
     src = path + ".pio/build/esp8266-ssd1306/firmware.bin"
     dst = path + "firmware/" + versionout
     os.rename(src, dst)
-    gzip_bin(dst, dst + ".gz")
     
     versionout = version[:-1] + "_esp8285_" + sha + ".bin"
     src = path + ".pio/build/esp8285-release/firmware.bin"
@@ -80,19 +77,16 @@ def readVersion(path, infile):
     src = path + ".pio/build/esp32-wroom32-release/firmware.bin"
     dst = path + "firmware/" + versionout
     os.rename(src, dst)
-    gzip_bin(dst, dst + ".gz")
 
     versionout = version[:-1] + "_esp32_nokia5110_" + sha + ".bin"
     src = path + ".pio/build/esp32-wroom32-nokia5110/firmware.bin"
     dst = path + "firmware/" + versionout
     os.rename(src, dst)
-    gzip_bin(dst, dst + ".gz")
 
     versionout = version[:-1] + "_esp32_ssd1306_" + sha + ".bin"
     src = path + ".pio/build/esp32-wroom32-ssd1306/firmware.bin"
     dst = path + "firmware/" + versionout
     os.rename(src, dst)
-    gzip_bin(dst, dst + ".gz")
 
     # other ESP32 bin files
     src = path + ".pio/build/esp32-wroom32-release/"
diff --git a/src/app.cpp b/src/app.cpp
index 7b7c6e0e..96b2e83e 100644
--- a/src/app.cpp
+++ b/src/app.cpp
@@ -33,10 +33,9 @@ void app::setup() {
 
 
     everySec(std::bind(&app::tickSecond, this));
-    everyMin(std::bind(&app::tickMinute, this));
-    every12h(std::bind(&app::tickNtpUpdate, this));
     every(std::bind(&app::tickSend, this), mConfig->nrf.sendInterval);
     #if !defined(AP_ONLY)
+        once(std::bind(&app::tickNtpUpdate), 2);
         if((mConfig->sun.lat) && (mConfig->sun.lon)) {
             mCalculatedTimezoneOffset = (int8_t)((mConfig->sun.lon >= 0 ? mConfig->sun.lon + 7.5 : mConfig->sun.lon - 7.5) / 15) * 3600;
             once(std::bind(&app::tickCalcSunrise, this), 5);
@@ -131,6 +130,15 @@ void app::loop(void) {
     mMqtt.loop();
 }
 
+//-----------------------------------------------------------------------------
+void app::tickNtpUpdate(void) {
+    uint32_t nxtTrig = 5;  // default: check again in 5 sec
+    if (mWifi.getNtpTime())
+        nxtTrig = 43200;    // check again in 12 h
+    once(std::bind(&app::tickNtpUpdate, this), nxtTrig);
+}
+
+
 //-----------------------------------------------------------------------------
 void app::tickCalcSunrise(void) {
     if (0 == mTimestamp) {
@@ -139,7 +147,7 @@ void app::tickCalcSunrise(void) {
     }
     ah::calculateSunriseSunset(mTimestamp, mCalculatedTimezoneOffset, mConfig->sun.lat, mConfig->sun.lon, &mSunrise, &mSunset);
 
-    uint32_t nxtTrig = mTimestamp - (mTimestamp % 86400) + 86400; // next midnight
+    uint32_t nxtTrig = mTimestamp - ((mTimestamp + 1000) % 86400) + 86400; // next midnight
     onceAt(std::bind(&app::tickCalcSunrise, this), nxtTrig);
     if (mConfig->mqtt.broker[0] > 0) {
         once(std::bind(&PubMqttType::tickerSun, &mMqtt), 1);
diff --git a/src/app.h b/src/app.h
index e494cf91..d29e6402 100644
--- a/src/app.h
+++ b/src/app.h
@@ -143,15 +143,7 @@ class app : public ah::Scheduler {
             }
         }
 
-        void tickMinute(void) {
-            if(0 == mTimestamp) {
-                mUpdateNtp = true;
-            }
-        }
-
-        void tickNtpUpdate(void) {
-            mUpdateNtp = true;
-        }
+        void tickNtpUpdate(void);
 
         void tickCalcSunrise(void);
         void tickSend(void);
diff --git a/src/defines.h b/src/defines.h
index d223d764..866c4296 100644
--- a/src/defines.h
+++ b/src/defines.h
@@ -13,7 +13,7 @@
 //-------------------------------------
 #define VERSION_MAJOR       0
 #define VERSION_MINOR       5
-#define VERSION_PATCH       50
+#define VERSION_PATCH       51
 
 //-------------------------------------
 typedef struct {
diff --git a/src/utils/scheduler.h b/src/utils/scheduler.h
index d10b56fd..52cdc2b4 100644
--- a/src/utils/scheduler.h
+++ b/src/utils/scheduler.h
@@ -48,20 +48,28 @@ namespace ah {
             void loop(void) {
                 mMillis = millis();
                 mDiff = mMillis - mPrevMillis;
-                if(mDiff >= 1000) {
-                    if(mMillis < mPrevMillis) { // overflow
-                        mPrevMillis = mMillis;
-                        return;
+                if (mDiff < 1000)
+                    return;
+
+                mDiffSeconds = 1;
+                if (mDiff < 2000)
+                    mPrevMillis += 1000;
+                else {
+                    if (mMillis < mPrevMillis) { // overflow
+                        mDiff = mMillis;
+                        if (mDiff < 1000)
+                            return;
                     }
                     mDiffSeconds = mDiff / 1000;
-                    mDiffFraq    = mDiff % 1000;
-                    mPrevMillis += (mDiffSeconds * 1000) - mDiffFraq;
-                    checkEvery();
-                    checkAt();
-                    mUptime += mDiffSeconds;
-                    if(0 != mTimestamp)
-                        mTimestamp += mDiffSeconds;
+                    mPrevMillis += (mDiffSeconds * 1000);
                 }
+
+                mUptime += mDiffSeconds;
+                if(0 != mTimestamp)
+                    mTimestamp += mDiffSeconds;
+                checkEvery();
+                checkAt();
+
             }
 
             void once(scdCb c, uint32_t timeout)     { mStack.add(c, timeout, 0); }
@@ -105,6 +113,7 @@ namespace ah {
 
                     if(expired) {
                         (p->d.c)();
+                        yield();
                         if(0 == p->d.reload)
                             p = mStack.rem(p);
                         else {
@@ -122,6 +131,7 @@ namespace ah {
                 while(NULL != p) {
                     if((p->d.timestamp) <= mTimestamp) {
                         (p->d.c)();
+                        yield();
                         p = mStackAt.rem(p);
                     }
                     else
@@ -134,7 +144,6 @@ namespace ah {
             uint32_t mMillis, mPrevMillis, mDiff;
             uint32_t mUptime;
             uint8_t mDiffSeconds;
-            uint16_t mDiffFraq;
     };
 }
 
diff --git a/src/wifi/ahoywifi.cpp b/src/wifi/ahoywifi.cpp
index c8a10412..1ccede08 100644
--- a/src/wifi/ahoywifi.cpp
+++ b/src/wifi/ahoywifi.cpp
@@ -115,9 +115,11 @@ void ahoywifi::setupStation(void) {
 
 
 //-----------------------------------------------------------------------------
-void ahoywifi::getNtpTime(void) {
+bool ahoywifi::getNtpTime(void) {
     //DPRINTLN(DBG_VERBOSE, F("wifi::getNtpTime"));
-    time_t date = 0;
+    if(!mConnected)
+        return false;
+
     IPAddress timeServer;
     uint8_t buf[NTP_PACKET_SIZE];
     uint8_t retry = 0;
@@ -138,16 +140,16 @@ void ahoywifi::getNtpTime(void) {
                 secsSince1900 |= (buf[42] <<  8);
                 secsSince1900 |= (buf[43]      );
 
-                date = secsSince1900 - 2208988800UL; // UTC time
-                break;
+                *mUtcTimestamp = secsSince1900 - 2208988800UL; // UTC time
+                DPRINTLN(DBG_INFO, F("[NTP]: ") + ah::getDateTimeStr(*mUtcTimestamp) + F(" UTC"));
+                return true;
             } else
                 delay(10);
         }
     }
 
-    *mUtcTimestamp = date;
-
-    DPRINTLN(DBG_INFO, "[NTP]: " + ah::getDateTimeStr(*mUtcTimestamp) + " UTC");
+    DPRINTLN(DBG_INFO, F("[NTP]: getNtpTime failed"));
+    return false;
 }