One of the first games I 100% completed on my xbox. Note, it does have dlc achievements and requires multiplayer to finish but if you get a person it's not that bad.
This was definitely a slog to get through with some such as bad father. Not only do you need to wait 100 days (I think with sleeping it takes 20 minutes per day) but you can't die otherwise it resets. For me I just sat in a shack and ate berries while watching YouTube, BUT if you have a friend I could see it not being as bad. Same problem with the 50k steps achievement, etc.
Most of the achievements aren't that bad to be fair. Just rather boring. I will say it shouldn't take 85 hours if you're going straight for achievement.
Great Far Cry game but also great for getting achievements. It's pretty quick and can be done all on one file. Only advice I'd feel is needed is to try to get the early outposts done without being detected (total stealth) because one achievement requires all perks and one perk requires 2 outposts without detection. I didn't start that until only the late game outposts were available so it was much harder to achieve and could theoretically soft lock you (or maybe I'm just bad at stealth).
There is a few collectathons but there's no missables and it is worthwhile to do as it helps to explore the map.