substitution after time-out?

[akingsfan]

I have a substitution question. Team A is shooting two freethrows at the end of a game (3 seconds left) while down by three. They call timeout and during the timeout, the coach tried to sub but after the 45 second horn had sounded so they referees didn't allow them to come in at the time. My question is can those subs come in after the first free throw is shot? They were not allowed to and I was wondering if this was correct? Any comments would be appreciated. Thanks