As close to the move-out date as possible. If you can arrange it for the same day, then even better. The longer you leave it, the easier it will be for the tenant to claim that it is incorrect.
Furthermore, depending on the deposit scheme used, a landlord has only 10 days to return a deposit, so the quicker you perform the check-out inventory and agree on it with your tenant, the better, or you may find yourself in breach of the law.
