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Well usually casinos offers instant deposits and you can start playing right away.They only want a few confirmations before withdrawing and this amount is usually 3 confirmations.In case you win you just wait for the 3 confirmations and then can withdraw instantly.
As far as I know, in order for you to get and be able to "use" your withdrawals, you will be needing more than 3 confirmations from the blockchain of bitcoin. As I understand it, it is different from instant deposits in which most of the time 1,2, or 3 confirmations are enough to have the deposits credited to your casino wallet.