How long does "Instant" usually take ? (After 24h still pending)
Unless your withdrawal has been flagged to be reviewed manually, it should be processed in 15 minutes.
If your withdrawal has been flagged to be reviewed manually for any reason, you should see a message saying your withdrawal will take up to 24 hours.
Note that this is assuming their service is working as expected. In the past year, there have been many issues with the website and there have been many reports complaining about withdrawals taking much longer time to be processed.
The last time I requested a withdrawal from freebitco, it took around a week.