Hi Munir,
You can add a log entry to track the MAC-Moves and be notified as soon as the flapping starts.
Since this can add lot of log entries you can enable a syslog server or even increase the switch log buffer from 1000 to 20000.
If the flapping already started and if you didn't have those logs entries added, I don't believe you will be able to find the exact date/time.