A few hours is a pretty good amount of time.
I had a 3-hour gig on Sunday, and my fingers were fine. I've done 1-hour intense practice sessions that had my cats yowling, too (if the feet are dogs, the hands gotta be cats, right?). So it depends how hard you're working, of course (that gig was pretty chill, for example), and also if you're taking care to build up the calluses vs routinely overdoing it to the point of hot spots or even blisters.
We all like to think that if we power thru discomfort, we ultimately gain the greatest strength and endurance, but no--musicianship is tiny-muscle athletics. We have to train our body parts, quite carefully, and it's incredibly easy to abuse them even when we're well conditioned. The same was true with my embouchure when I was playing both oboe and trombone at a university level.
While my calluses are petite but well established (averaging an hour a day practice time), I can still easily make my plucking fingers feel uncomfortable and tender within 10-20 minutes if I abuse them. They're like lips that happen to be on my hand. (heh for the weird visual)
No shame in stopping practice when you feel your fingers have had enough, and indeed, that's THE right time to stop. Tomorrow's fingers will thank you for pacing yourself today!