In the regular season, if there's a defensive zone penalty with less than 30 seconds to go, it should result in a penalty shot, and no delayed penalty.
Imagine a scenario where a defensemen is about to take a shot from the point with 1 second remaining and then gets tomahawk slashed from behind and has his stick broken....and the game just ends and they give the slasher a penalty at the end of the game when it's too late.
I think that's a major flaw in the penalty system. Players are free to get late game penalties since it won't result in a full powerplay. Their options become, stop a legit scoring chance, or take a very short penalty.