Place the timestamp processing in order:
1) If no timestamp found, use the current system time when indexing the event.
2) Use TIME_FORMAT from to identify a timestamp in an event
3) If Splunk finds a time, but no date, try to find the date in source name or file name.
4) If Splunk cannot identify a date, use the file's modification time.
5) If no TIME_FORMAT is configured, try to automatically identify a timestamp from the event.
6) If no timestamp found, use the most recent timestamp.