I do about 3 hours of legit work when I'm in my usual situation (family, work), but I do way more when I'm alone, both on- and off-the-grid: 12 hours or even more (of course assuming that the problem I'm working on is workable and I don't hit any serious brick walls). My last superfocus period lasted for about two weeks, it happened when my family went on vacation, and I took a mini-vacation from work myself (though the task I was working on was pretty trivial). My longest superfocus period was about 45 days, it happened on a long off-the-grid vacation.