If you just do the story stuff you can probably do it before hitting the 5 hour mark. Took me 8 because I was dicking around with the side quests. the game makes it kinda ambiguous so I'll say it, not really a spoilers, but you can go back and do those side quests at any time.
Oh yeah I know I can repeat missions which is nice but you're talking about side-quests here so is it obvious when I'm doing story advancement vs side stuff? I'm asking because in MGS for example I just rushed the main missions and it was obvious then since you had to pick them, side stuff were literally called side-ops
Spoilers don't really bother me if you're having to spoil gameplay like "when you get to X place, that's chapter 3, etc" but still mark them since y'know, it's still spoilers
I'm talking about completing side missions you haven't picked up yet in that first area. The game makes it seem like you wont be coming back with one dialogue line but you will be.
Story advancement usually means you're going in a direction you havent been before. So if you go to an area outside of the Chiral Network that's probably a story mission.
But ch3 *spoilers for gameplay mechanics* introduces road paving, fast travel (allowing you to go to the first area) and vehicle blue prints that makes doing the ch2 side quest less time consuming and more fun imo. ---