This question can only be answered by your snake.
Observe it, let it tell you when it's had enough handling. For the first 6 months I had him, it was maybe 10-15 minutes until he got antsy and I returned him to enclosure. 2-3 times per week. Usually at night (after 9 pm), with the room lighting low.
Last night I had my guy out for about an hour which was:
5-10 minutes in hands, until he was calm. Put him down on sofa for a few minutes while I misted the enclosure and then
10-15 minutes of 'The Royal (Ball) Treatment' - wiped him down with a moistened paper towel, and used a towel to dry him off afterwards. He was wrapped around one arm, not moving much so I think he enjoys this. Then, put him down on sofa for a few minutes while I tossed out the paper towel. (I'll try video recording this next time - maybe Sunday night).
20 minutes alternately handling/playing/letting him roam around on sofa and floor - and me. I had him around my neck a few times when needing to go from one room to another.
Then I noticed he was trying to pull away and get away from me with a little more effort/urgency, so it was time to return him to tank. The terrarium has sliding doors so I held him near the door and let him 'decide' to go back in at his own pace.
EDIT: but each snake/owner is different; some people handle their snake almost every day, others leave their pet alone and only take it out for feeding in a separate tub, showing to friends, or when cleaning the cage.