I used the instant withdraw to send to this address bc1qnf87mmeqj9h8vap6ss6775h6h5074cdmdwzdht and after way more than 15 minutes the pending withdrawal warning on the website disappeared but no trace of the transaction nor of the BTC, how long it needs to transact? is the address i put in not compatible in some way?
If the address was not compatible, the system would have told you that you put a wrong address, there is no way they will process a withdrawal request to a wrong/unsupported address where the user was not alerted of the with an error message, that is so unprofessional.
What might be the problem is that in the current freebitco, the instant withdrawal seem to no longer work, so, using that feature is meaningless cus, there is no way you are going to get your withdrawal request instantly processed, what I did suggest you do is be patient, copy the address you requested that your funds be sent to, and paste/search it on any of the bitcoin blockchain Explorers to see if the funds has been sent there and it's yet to reflect on the site.
If no funds have been sent, then be patient until you receive the funds.