My Dumeril's Boa is still young, but she gets a little stressed after 20 minutes or so. She's getting better with each handling though and by the time she's an adult she should outgrow the youngling nervousness. My BCI is only a couple of months older though and even after having her out for an hour or more she will fight me when I try to put her back in the cage. After holding a gorgeous six foot female I finally understood why having another person can come in handy...it's not the handling that's a problem, it's putting them back! Lol. It was much easier with someone else there to open and close the doors.But in my experience, the BCIs seem to really enjoy being out and about for the most part. Of course, every animal is entitled to bad days, and on those days they should be left alone except for essential care tasks.
It really depends on the individual animal.