the play, he could look up at the time clock and wait until 10 seconds has run off the play clock. If the defense doesn't sub within the first 5 seconds, then he could move early and let the offense snap the ball. Basically the defense has 5 seconds to decide and then a total of 10 seconds to sub.

10 seconds might not be the number - maybe it's 12 or 15 seconds - whatever, just pick a time so it's consistent.