Block time is one minute. On average it will only take a one minute a transaction to first appear in the block chain; however, exchanges usually will require at least 18 confirmations (blocks) before adding funds to your account, and the standard wallet requires tbd confirmations before considering received coins to be available for use.

A time of 10-20 minutes is generally the longest length of time you should consider waiting if your transaction isn’t confirmed in a couple of minutes.