[time] Point to valid IANA timezone list on validation failure (#15110)

esphome/components/time/__init__.py

@@ -284,13 +284,23 @@ def validate_tz(value: str) -> str:
     tzfile = _load_tzdata(value)
     if tzfile is not None:
         value = _extract_tz_string(tzfile)
+        is_iana = True
+    else:
+        is_iana = False
 
     # Validate that the POSIX TZ string is parseable (skip empty strings)
     if value:
         try:
             parse_posix_tz_python(value)
         except ValueError as e:
-            raise cv.Invalid(f"Invalid POSIX timezone string '{value}': {e}") from e
+            if is_iana:
+                raise cv.Invalid(f"Invalid POSIX timezone string '{value}': {e}") from e
+            raise cv.Invalid(
+                f"Invalid POSIX timezone string '{value}': {e}. "
+                f"If you meant to use an IANA timezone, check the list of valid "
+                f"timezones at "
+                f"https://en.wikipedia.org/wiki/List_of_tz_database_time_zones"
+            ) from e
 
     return value