diff --git a/src/time_manager.cpp b/src/time_manager.cpp
index 6f0144c..17a8110 100644
--- a/src/time_manager.cpp
+++ b/src/time_manager.cpp
@@ -1,10 +1,15 @@
 #include "time_manager.h"
 #include "config.h"
 #include <time.h>
+#ifdef ARDUINO_ARCH_ESP32
+#include <esp_sntp.h>
+#endif
 
 static bool g_time_synced = false;
+static bool g_clock_plausible = false;
 static bool g_tz_set = false;
 static uint32_t g_last_sync_utc = 0;
+static constexpr uint32_t MIN_PLAUSIBLE_EPOCH_UTC = 1672531200UL; // 2023-01-01 00:00:00 UTC
 
 static void note_last_sync(uint32_t epoch) {
   if (epoch == 0) {
@@ -13,6 +18,32 @@ static void note_last_sync(uint32_t epoch) {
   g_last_sync_utc = epoch;
 }
 
+static bool epoch_is_plausible(time_t epoch) {
+  return epoch >= static_cast<time_t>(MIN_PLAUSIBLE_EPOCH_UTC);
+}
+
+static void mark_synced(uint32_t epoch) {
+  if (epoch == 0) {
+    return;
+  }
+  g_time_synced = true;
+  g_clock_plausible = true;
+  note_last_sync(epoch);
+}
+
+#ifdef ARDUINO_ARCH_ESP32
+static void ntp_sync_notification_cb(struct timeval *tv) {
+  time_t epoch = tv ? tv->tv_sec : time(nullptr);
+  if (!epoch_is_plausible(epoch)) {
+    return;
+  }
+  if (epoch > static_cast<time_t>(UINT32_MAX)) {
+    return;
+  }
+  mark_synced(static_cast<uint32_t>(epoch));
+}
+#endif
+
 static void ensure_timezone_set() {
   if (g_tz_set) {
     return;
@@ -25,24 +56,31 @@ static void ensure_timezone_set() {
 void time_receiver_init(const char *ntp_server_1, const char *ntp_server_2) {
   const char *server1 = (ntp_server_1 && ntp_server_1[0] != '\0') ? ntp_server_1 : "pool.ntp.org";
   const char *server2 = (ntp_server_2 && ntp_server_2[0] != '\0') ? ntp_server_2 : "time.nist.gov";
+#ifdef ARDUINO_ARCH_ESP32
+  sntp_set_time_sync_notification_cb(ntp_sync_notification_cb);
+#endif
   configTime(0, 0, server1, server2);
   ensure_timezone_set();
 }
 
 uint32_t time_get_utc() {
   time_t now = time(nullptr);
-  if (now < 1672531200) {
+  if (!epoch_is_plausible(now)) {
+    g_clock_plausible = false;
     return 0;
   }
-  if (!g_time_synced) {
-    g_time_synced = true;
-    note_last_sync(static_cast<uint32_t>(now));
+  g_clock_plausible = true;
+#ifdef ARDUINO_ARCH_ESP32
+  if (!g_time_synced && sntp_get_sync_status() == SNTP_SYNC_STATUS_COMPLETED) {
+    mark_synced(static_cast<uint32_t>(now));
   }
+#endif
   return static_cast<uint32_t>(now);
 }
 
 bool time_is_synced() {
-  return g_time_synced || time_get_utc() > 0;
+  (void)time_get_utc();
+  return g_time_synced && g_clock_plausible;
 }
 
 void time_set_utc(uint32_t epoch) {
@@ -51,8 +89,12 @@ void time_set_utc(uint32_t epoch) {
   tv.tv_sec = epoch;
   tv.tv_usec = 0;
   settimeofday(&tv, nullptr);
-  g_time_synced = true;
-  note_last_sync(epoch);
+  if (epoch_is_plausible(static_cast<time_t>(epoch))) {
+    mark_synced(epoch);
+  } else {
+    g_clock_plausible = false;
+    g_time_synced = false;
+  }
 }
 
 void time_get_local_hhmm(char *out, size_t out_len) {