I handle all of mine at least once a week. I take them out when I'm doing my spot clean. I like to handle the juveniles a few times a week just to get them accustomed to being handled.
As far as time of handling, with the young ones, typically 5-10 minutes, but with my big guys, I can leave them out for a bit. They are more laid back and are so used to being handled at this point that I think they actually look forward to it!
I like to weigh them, measure them, and let them crawl around a bit. It's nice having them tolerant of it because people always want me to bring them out when they come over for a visit. It's nice knowing I'll have friendly snakes to share.

I hope that helps!