Hugo Strange announced over the intercoms in Arkham City that there were 10 hours left until Protocol 10 would be initiated. I'm currently in the Steel Mill heading to Joker right now, and while I was in there, he said that there were only 9 hours left.
I'm assuming that because this is an open world game, it's not forcing an actual time limit in real world time (though please correct me if I'm wrong). However, I'm wondering how exactly it advances during gameplay.
Does the countdown only advance while you do the main storyline missions or will other things, like doing sidequests, collecting X amount of Riddler trophies, etc. also affect it?