This one has always annoyed me. There are a lot of delayed calls in sports - off sides in hockey, most things in soccer, obstruction calls in baseball. Let it play out - if the defensive team gets possession let them play the advantage. Different if it is a foul or traveling where they have to stop the game, but a shot clock violation with a live ball would be easy to make a delayed whistle.
I will say after watching the replay that in this case, Indiana made no effort to get back on D, figuring the shot clock would go off, so perhaps Chalmers wouldn't have gotten a sure uncontested layup if the rules were different. Obviously, the Heat were killed more by a lousy Wade shot and two James turnovers on the last 3 possessions.