I have been on this kind of situation before and I know how it felts like it is really annoying and you feel like you are wasting your time, money and energy, but I know this is to prevent from excessive withdrawing since there are gamblers who transfers big amount of money inside their casino and will try to win whatever they are offering either the pot money and will just withdraw immediately after winning. They are preventing this kind of scenes from happening that is why mostly you have to control how much you are going to put inside the casino just in case they will put this "lock period" strategy.