Probably every few days I need a little time, maybe half an hour or so at least, to myself. There are certain people - my mom, dad, brother, boyfriend - that don't make me feel like I need to recharge at all. Most other interaction I do need time away from, if only to recenter myself. For me it's less about being around unpleasant people and more about needing some time to be able to prioritize my needs, because I'm generally inclined to prioritize others' needs first (it usually takes less energy for me to help someone else than to do my own thing). Like others have mentioned, I like to be around people even when I'm having my down time. Right now my boyfriend is across the room playing video games and that works fine for me.
The only time I really like to be totally alone is in the early morning, which I've always considered sort of a sacred quiet time, and I tend to get irritated with anyone breaking my early morning peace! I also like to experience nature alone - quasi-spiritual natural experiences like the Northern Lights, sunrise or set, meteor showers, snow at midnight, etc. Someone else can be along with me only if they are quiet and reverent of it, too.
As for high-stress interaction where I have to be really "on" - around high-status people, or new people in a context where there is no set structure for interaction - I can do a few hours happily or a couple of days at most but then I want a big chunk of down time. At work where there is a set structure for what my role is and their role is then it's generally easy and pleasing, though I still am eager to come home to my comfortable, familiar loved ones at the end of the day.
Me too. Once I was in a foreign country with a reclusive flatmate and no internet access for two weeks. I ended up walking an hour to downtown every day just to use the internet cafe and interact with cashiers. I felt myself shrivel inside.