fix esphome reboots on no wifi

esphome/common/sntp_common.yaml

@@ -1,6 +1,6 @@
 ############################################################################################
 # SPECIFIC DEVICE VARIABLE SUBSTITUTIONS
-# If NOT using a secrets file, just replace 
+# If NOT using a secrets file, just replace
 # these with the values (in quotes)
 ###########################################################################################
 substitutions:
@@ -25,10 +25,10 @@ time:
   # Change sync interval from default 5min to 6 hours (or as set in substitutions)
     update_interval: ${sntp_update_interval}
   # Set specific sntp servers to use
-    servers: 
+    servers:
       - "${sntp_server_1}"
       - "${sntp_server_2}"
-      - "${sntp_server_3}"    
+      - "${sntp_server_3}"
   # Publish the time the device was last restarted
     on_time_sync:
       then:
@@ -65,11 +65,27 @@ text_sensor:
     update_interval: "1min"
     entity_category: diagnostic
     lambda: |-
-      auto time_text = id(sntp_time).now().strftime("%H:%M:%S - %d-%m-%Y");
-      return { time_text };
+      // If SNTP time is valid, show real time/date.
+      if (id(sntp_time).now().is_valid()) {
+        auto t = id(sntp_time).now().strftime("%H:%M:%S - %d-%m-%Y");
+        return { t };
+      }
+
+      // Fallback: show internal clock based on current_mins (minutes from midnight).
+      // NOTE: current_mins is expected to be a global defined in the main device YAML.
+      int mins = id(current_mins);
+      if (mins < 0) mins = 0;
+      if (mins >= 1440) mins = mins % 1440;
+
+      int hour = mins / 60;
+      int minute = mins % 60;
+
+      char buff[32];
+      snprintf(buff, sizeof(buff), "%02d:%02d (fallback)", hour, minute);
+      return { std::string(buff) };
 
   - platform: template
     name: "Time: Sync Status"
     id: time_sync
     update_interval: "1min"
-    entity_category: diagnostic
+    entity_category: diagnostic