Typically Bitstop transactions are broadcast to the Bitcoin Network instantly. So you should see your purchase reach its destination within 1-2 minutes after it’s completed. In times of network connection Bitstop will bunch smaller transactions and broadcast those every 20 minutes.
Once your bitcoin is sent you’ll see it in your wallet immediately. Once the bitcoin are in your wallet it can still take some time to receive one confirmation from the Bitcoin Network. Bitstop attaches enough fee to receive a conformation within an hour of your transaction being sent to the network. This can be variable depending on the activity on the Bitcoin Network.