Judging by my steam time, I spent no more than 18 hours in Act 2, and no more than 57 hours in Act 1. A lot of that time was spent reloading to see different outcomes and returning to areas I had already been to see if I missed something.
I did everything on the "Act 2 Checklist" on the subreddit, including things that were not listed on the Act 2 Checklist like the "Cursed Fishing Shack" (being vague on purpose). I'm not going to list other things that I did that were not on the checklist because of spoilers. All told, 3 of those 18 hours I probably spent backtracking and checking for secrets. I concur with someone else in the thread who said that Act 2 is realistically 15 hours of content. It is underwhelming because Act 1 is more than 3 times its size in choices and character development and exploration and diverse locations.
To clarify any confusion in the thread, the game defines Act 2 as solely the Shadow-Cursed Lands.
EDIT: Independent of the time I spent on each act with my backtracking and reloading, if I were to guess how much content there is if a perfectly efficient player were doing a quick 100% run of each Act, I'd say Act 1 is 30-40 hours of solid and highly reactive content, while Act 2 is 10-15 of swiss cheese content that is barely reactive, except for 2-3 events.
