Does anyone knows how long the bonuses you get from resting at inns last? Is there a set duration of x hours? Sometimes the bonuses vanish when I camp out in the wild, but other times they're still there when the party wakes up again.

Basically it'll last through one other rest and then expire if you rest again. Assuming time passes as you're playing, I'd say 24 hours?

I think that resting bonuses from inns last until you rest

Resting bonuses from your stronghold last for more rests. How much exactly, I dunno, I frequently sleep inns cause the bonuses are much better.

 

As far as I'm aware, there's no set duration of x hours, but it is defined by your resting/camping.