Sellers normally release bitcoins as soon as possible after getting paid, which may need 1~2hours. If you have paid but still waiting for btc, you don't have to worry because all the online transactions are protected by escrow and sellers can't take your bitcoins away.
If any problems appear during the transaction, seller refuses to release the bitcoins, you can make an appeal on the transaction and Customers Service of BitcoinWorld will solve the problems.
If bitcoins are released from escrow or traded without escrow, the appeal will not be successfully made.
If your transactions are appealed, you will got the messages and emails. Mostly, once you make the appeal, you can get the notice of the other party of transaction. The appeal will be solved between 24 hours ~ 48 hours.