I have replayed Black Geyser. The critical path with claiming the stronghold was 7.5 hours. There are some continuity bugs, but overall it was fun. Not doing the time-travel quest turned out to be a mistake - it allows to skip a large dungeon and an otherwise-unavoidable boss. I have also managed to get the king killed prematurely, but the game softlocked due to it, so it took a few more hours to do it "properly".
The writing occasionally makes me want to cry, but there are also the obviously OOC options, so it kind of balances out. Granted, in the dialogues with the king, choosing them quickly leads to combat and the infinite guards teleporting in.