If the guy clearly indicated that he wanted you to instant transfer instead of standard transfer, whatever that is, then you should have done that. To transfer it with a standard transfer could mean that he loses liquidity for the time the money is held in escrow and not be able to trade with the money that he would ahve otherwise been able to make further trade with.

Ask him to either refund or wait till the funds hits his account. If he doesn't want to then you have to start disputing.