I am a rescue home so my daily amount varies, its very different from a pet home. When I was a pet home it was Out time for at least 1-2 hours a day, as a group, with individual time when they wanted it. Some just want to run and explore rather than take time with you, but will do run-by visiting, which is fine
My husband and I used to have our two rat boys out at least 2 or 3 times a day for different periods of time, depending on what the boys wanted. Usually at least 30 minutes a time, up to an hour at a time. Sometimes they played on our bed with their blankets and toy boxes for a long time, or enjoying play time with mom and dad, with us laying on the bed and them having fun crawling over us and playing, and other times they were in the mood to just be carried around the house, getting a house tour from our shoulders and getting snuggles.
I take my girls out for about two hours most days. The two twins don't really care for much one on one attention and will just run by occassionally while they're running around playing, but Penny and Lila spend almost the entire time out with me.