Clock stops when - ball heading out of bounds

[OYC2013]

Let’s say there are just seconds left in the game. Shot goes up and player on winning team gets the rebound and throws the ball toward the end line. Ball bounces in play and takes a high bounce toward the stands. Theoretically, a player could attempt to leap from in bounds and attempt to bat the ball back into play without the ball every hitting anything out of bounds and the clock would , of course would keep running. But let’s say the ball bounced high enough to actually stay on the air high enough to not touch anything in the stand for let’s 3 seconds, which by that point the game clock could go off ending the game.
I see a lot of refs blow the whistle stopping the clock while the ball is still in the air prior to the ball actually hitting something out of bounds.
Granted, in my example above, it’s not very likely that a player could leap from in bounds, stay in the air, and actually have a chance of batting the ball back into play, but shouldn’t the clock run until the ball hits something out of bounds? I guess it’s similar somewhat to a player throwing the ball toward the roof of a big arena, where it never hits any structure but takes 4 seconds or so to finally come down , this running out game clock in the process.
So, do you wait to blow the whistle until the ball actually touches something out of bounds in my example above?