Let me start by saying that I'm not a writer but a lifelong bookworm.
As such, I cannot say if there are any conventions or rules that publishers expect but if there are authors clearly don't follow them! ;-)
As Quentin has already pointed out there are stories that use only one setting:
- almost all of Daniel Defoe's "Robinson Crusoe" takes place on one island (which only one main character!)
- Stephen R. Donaldson's massive fantasy duology "Mordant's Need" of about 1,300 pages is almost entirely set in a castle
- Umberto Eco's "The Name of the Rose" almost exclusively takes place in a monastery
- the characters of Stephen King's "Shining" spend most of their time in a hotel and in his "Under the Dome" a small town is trapped under an impenetrable dome within which all the action takes place
- You could even argue that Agatha Christie's "Murder on the Orient Express" or even Herman Melville's "Moby Dick" only have one setting. Sure, physically they move around but the characters are in a way limited to their mobile setting (train / ship).
As is Pi in Yann Martel's "Life of Pi".
Well, you get the idea. ;-)
To me as a reader, this has never been an issue I've given much thought.
I'd say, keep your characters in a given setting as long as it is necessary for the story. I guess, this is a judgment call and if you have the feeling that it might be too long, maybe try to get feedback from trusted test readers.
For me, the much more important question is whether the narration can keep my interest. Staying in one setting is not a problem if the author makes it interesting enough. I loved Ken Follett's "The Pillars of the Earth", a hefty novel which tells a sprawling story set in and around a medieval town (and its cathedral), but I also loved, despite its historical inaccuracies, Noah Gordon's "The Physician" which follows the main character from his early years in England through Europe all the way to Isfahan in Persia.
I was never bored for a page in either novel, even though the first is limited to one place, more or less, and the second changes scenes frequently. I wasn't bored because the writers managed to keep me engaged in the story.
Don't worry about how many chapters your character remain in a setting.
Worry about keeping your readers engaged! :-)