If somebody send Btx to my encrypted wallet, can i decrypt the wallet after 12 hours for example and to receive these coins with no problems, i mean is there some period after which the transaction will be cancelled if we dont decrypt the wallet?
there is no relation between encrypted wallet and receiving coins.
even if you don't sync your wallet, your address would still receive coins just fine no matter what
just that when you're not synced you won't see it in your wallet (but it's there)
and you have to decrypt your wallet for awhile to be able to send out coins
I never encrypt my wallet, so I'm not 100% sure about decrypt before sending coins
If the wallet is encrypted then you'll need to enter the password to send coins out of the wallet.
I'm not sure that there is any feature that allows anyone to decrypt a wallet once its been encrypted (maybe you meant something different?).