I have been paying attention to time on the clock when teams break the huddle for the last four weeks or so. It has been a bit of a compulsion. It is very rare to get a positive play coming out of the huddle when you are that late. You need to call time out or there is very little chance and much of the time you take a penalty. If there are fewer than 18 seconds or so when your subs are in and you close the huddle it is pretty much not ever going to happen.
Unless you are fucking Bills playing the Patriots.