B Conference during sub for A1's fifth foul

[hawk65]

I think I know the answer to this but am seeking confirmation. A1 commits his fifth foul; table buzzes the horn and notifies the officials it is his fifth foul; officials notify A coach. As soon as he understands it is A1's fifth foul, B coach calls his players to the front of his bench hoping to get a few seconds of conference. But A coach immediately sends in a substitute and doesn't want to take any of the allowed time to make this substitution. Officials tell B coach to have B team come right back on to the court. B coach argues he can take 20-30 seconds to confer with his players. I tell B coach "He [A coach] can take time to substitute but you can't be granted the time if he substitutes immediately." B coach gives me a doubting look and reluctantly sends his players back out. Was this the correct application of the rules?