Hurry Up Situation!

[Nyjets]

Here is the play regarding a hurry up situation. Team A doesn't have any timeouts remaining, and just gained a first down inbounds. The clock is stopped to move the chains, but will start with the ready for play. Team A comes up to the ball and gets set with the snapper placing his hand on the ball. The umpire tells the snapper to wait for the whistle before snapping the ball. The very moment he hears the whistle blow, he snaps the ball and the QB spikes the ball immediately. Is this a legal play? Does the snapper have to wait for any certain amount of time after hearing the ready before snapping the ball? Remember, all members of the offense were set and just waiting for the whistle to blow. Your thoughts will be appreciated!