From what I've seen, there is no option for this. I feel it has to do with the fact that due to line changes and the option to sim thru time not on ice, you dont ever really play the full 20 mins. I know the time is shortened if you play as a goalie, as they never are off the ice. You could always play for lets say the first period, then pause and quit game, which will sim the rest of the game for you. Or just sim every second game or so.
