Completely-alone-no-contact-at-all, hmm, a day or two? It's not uncommon for me to not leave my apartment for a (couple) day(s), and my only contact with the outside world be internet forums, and a phone call from my mother, or my boyfriend.
Contact-with-people-but-limited-strictly-social-interaction, about a week. As in, going to school, and running errands and things that obviously require talking to people, but not doing anything specifically social, except the odd phone call.
On the flip side, the most time I can spend constantly around social people is a day or two before I need some time by myself. (For example, I love my boyfriend's family, but if I spend a weekend with them, I need to hide by myself for the next day to recharge.)
And I don't do purely social things, more than two or three times a week. More is too much, and I need my me-time.
I am a solitary extravert, I believe.
I don't have any single person that I am close to/friends with, so my social interaction is limited to co-workers and bank tellers/cashiers when I run errands. I have a habit of going maybe 2 or 3 times/week to sit at the cafe and pretend to read (can't concentrate well enough to read in public anyway) because I like the feeling of just sitting there in proximity to many other people, even if we don't interact. If I couldn't do this, and was in some kind of solitary confinement, I could go maybe a month before I would start to feel at a loss.
If I could bring my dog and cat, this would certainly change things.
I already get more time alone than I want or need, so I haven't felt the need to "get away" from people when I've been with them, in a very long time. IIRC, when I was more social, the down time I got at night was enough. There were few times when I had to abruptly leave some social thing because I felt too drained, and usually, that had more to do with something else, like being stressed or already tired, than for having been with other people.
edit: I change my mind. I'm not an extravert; I'm just bad at introverting.
Depends how you define human contact. 90% of my interaction with humans happens from behind a keyboard. With that interaction, I would happy going months without actually hanging out with someone in person.
“Everybody has a secret world inside of them. All of the people of the world, I mean everybody. No matter how dull and boring they are on the outside, inside
them they've all got unimaginable, magnificent, wonderful, stupid, amazing worlds. Not just one world. Hundreds of them. Thousands maybe.” -Neil Gaiman
Introverts: How long can you without human contact before you start to feel off?
Can't really say, haven't experienced any seriously prolonged periods without direct human contact. I live alone but I still have to go for grocery shopping at least once a week, so that's human contact right there whether I want it or not, even if it is indirect or not really on a deeper personal level. Most of my interaction happens online or by phone, though.
If I didn't have people in my life whom I'm attached to on a deep personal level, I could probably go on without human contact for a very long time. I have gone without direct contact for a week or so and I felt fine. I'm a very private person at all times and I don't desperately need a lot of human contact anyway. Usually I don't even notice how long it's been. However, I can say that my anxiety definitely heightens after a longer period without direct human contact, I feel out of place around humans then and it takes a while to get used to it, so it's better to have contact on a regular basis than not have it. Or something like that.
For me I can go for about a day without human contact (and I don't consider going to the grocery store really genuine human contact), after more than a day without people I quickly start feeling depressed. I am certainly an introvert but also the Fe and sx needs people contact or I start feeling off. Some people in this thread are describing that they could go without people contact for a week, despite being an introvert that sounds like hell to me.