Depends on mod conflicts (if you've like 60+ mods running simultaneously) and on the computer specs.
However I got beefy computer on last summer, so it won't break if I get bit crazy with the settings - as usually.
I have crashed few times, when doing mob battles like one town vs another or spawned over 25 giants, 25 dragons and 100 guards at once.
Have completed main quest for 2 times and now doing basically everything else - partying up I mean.
Like; Trying my best at making Skyrim not to feel like a adventure game... (making it to be dating sim), been changing draugr's to santa's and some less harmful creatures, randomized the climate, made myself king, enslaved whiterun, dropped the framerate with 3k textures, maxing out my render distance, added grass... ''resuited'' some npc's, made them marriable, jailed Heimskr, drived with car, rided with dragon, died when trying to surf on the waterfall, used mini-Sheogorath's as bow ammo and managed to update npc's dialogue options without killing my memory/graphic's card yet.
I can't really enjoy Fallout 4, because lore doesn't fit on my playing style, not enough dialogue ingame and so far haven't managed to port my character from skyrim on it.
Around 58 hours on FO4 anyways.
Been lately bit busy.
Best thing ever to do, is to use a custom race and raid with a moose, lead the army of giant chickens to blow up Imperials, then drown their city with watermelon's (can be done only with console command).
In my case; Lunari race.