Watching the PSU-Nebraska game.  Nebraska's offense sends in a late sub with 13 on the play clock.  The official immediately moves to the behind the center to prevent the snap in order to allow Penn State's defense time to make a substitution (by rule).  

A PSU defender runs in from the sideline, then runs off, then runs in again.  All the while, the official is preventing Nebraska from snapping the ball.  All 13 seconds of the play clock have now run out and Nebraska calls a time out.

Had they not called a time out, would they have gotten a delay of game?  How much time is the defensive sub allowed to waste in that case?  

I've seen this more frequently.  It seems like defenses are taking advantage of the rule.  If the offense had no time outs left, it seems like they would almost be forced not to sub in a player or risk a delay of game.