The time they need out is pretty much dependant on how much time you have - how many groups you have to let out, and how much each individual is in need. But how big their cage is, how it's equipped, and how much they amuse or enliven or comfort each other is a big factor.
I guess your intent is what's the least adequate time to take care of a kid's needs for outtime and time with you so you can go over but not under?
Far as individuals - My old Astoria never comes out with the others when the door is open, I would take her out and have a huggle and she was cool but soon as I put her down - back to the cage, so I stopped taking her out (she's not anti-social - I pet her when she's out of the hidey-houses in the cage and she closes her eyes and loves it.) She just doesn't need or want out-time.
Summer was sick and knew how to get to the bed when their door was closed while the others didn't. She lived on my bed, she needed to be out most all the time.
They need stimulation - mentally always, physically according to their age and capability. The more the space & interests of their cage and their cagemates can cover the the less they need from you. Sometimes you need their company more than they need yours :lol: . But they need you to stay human-comfy.
In all cases the more time you can give them the better, but I've left the cage open all day when I have a bed day and my most energetic kids only do about 3/4 hr. tops before they either go home or crawl under their bed-blanket and nap.
Healthy mid-age kids will have a blast being out but a-ok to go home in half an hour if you have great interaction time with them.
The youngest need the most stimulation and a busy cage - meaning other young'uns and/or lots of stuff to climb and explore. The cage's interests & activity things are more important than the time-out physically, but not emotionally. They just need to enjoy your company, and any that are not human-ok need some individual time, I try to focus on the bonding more than the out-time, they'll get in the raising heck & rough-housing in the cage.
Sick ones or Loner ones always need most. Loners for stimulation, and old or sick for help and/or comfort.
Old and/or sick need you more than they need an interesting environment, they get more emotionally needy of you than the group at that time (tho a cuddly cagemate is the best thing you can give them as you can't be there all the time). They need you for physical exercise & ability & clean-up and special feeding as well as emotional stuff. They need somejust-cuddle time with you after the meds and the clean-ups are done. So they need more time out to fit that all in. And more than one session. At least a couple half-hours a day.
I know, this was a simple question - but it probably is the question that has the least 1-proper-answer that you could ask.
Personally, I start with my most needy and whatever energy I have left I give to the rest. :wink: