This varies with each of my snakes (all different species), but since you're asking about BPs I'll limit my answer to my BP.
My BP is super chill, so he tends to be out longer than my others, but not more often. He comes out 3-4 times per week, obviously avoiding shed time and digestion time. On average he's probably out 20-30 minutes, but sometimes shorter. Since he's so chill, he's ok out a bit longer. But I cut handling sessions short if he seems to be "just not feeling it".