While actively dating? A few weeks. While long-distance-I-have-someone-at-home-dating? A few months.
That's more about me, than them, though. As in that's pretty much my upper limit outside of marriage & vows to still consider the person as someone I'm dating/in a committed relationship with. I can be f*ckbuddies or friends with someone I might only see once every few years, or a few weeks here / a few there, but my actual preference is "Some people call it codependent, we call it teamwork" version of live/work/play damn near 24/7/365.
It's a strange dichotomy, for me, because I isolate like f*ck as a sufferer, and have very little problem with other people isolating within my tolerance range, as a supporter. But the rest of the time I damn near keep the people closest to me all but in my pocket. I like to be able to reach out and touch the people I love, or at least have eyes on, the vast majority of the time.
One of the hardest things for me, in a relationship is having different jobs. It's a lot easier for me to live/work/play with someone 24/7 & be taking periodic breaks than it is for me to be breaking each and every single day :confused: Cough. I tend to be a little all or nothing, though.
The only person I very dated for more than a minute that didn't share that kind of patterning with me (both of our intense + isolate fell within the others tolerance limits) was my exHusband. But that was a shitshow from start to finish. If it weren't for my kid, we'd never have been together for more than a minute, to begin with. Hell. I tried to break up with him whilst pregnant. A few times, come to think of it. But after my kiddo was born all of the intollerable about my ex barely even registered, anymore. It's strange how kids do that; completely alter the needs&wants of the adult relationships around them (at least in some cases).