What is the timeframe to be able to reverse provisional credit on a POS transaction?

Assuming your dispute is covered by Reg E, you must complete your investigation on a POS transaction within 90 days from the date of consumer notice. If you are denying a claim, the provisional credit must be revoked prior to this time.
If you receive evidence to support the fact that the transaction was authorized after 90 days and the credit is final, you can only debit the account with your customer's permission.