We did ours in the summer……and some in the early fall.
PLEASE do your homework and make sure you have an appointment, as well as tour, during the summer. Often, the tour guides are faculty kids who are in school. They are the only ones around.
I would say that 2 is the max in CT and some parts of MA. But that is pushing it. You cannot expect to tour MSX and St Paul’s in one day. The drive is too long and the tours/interview/etc take longer than you realize. When we went to DA for a summer tour, the office made us wait in the nice waiting room (a former library) for almost an hour after the scheduled time. Kiddo later became a tour guide and made some changes to this problem (thanks, Kiddo!). At Choate - no tour guide showed up that day, so no tour that day…so that was really quick. At Groton we waited almost an hour past the scheduled interview time. It was cool though how they had the interviewees names written in calligraphy and posted on the door….got to check out where the competition was from 
Hotchkiss was on time and most welcoming….we toured Hotchkiss and Taft in one day. Hotchkiss wins for best admissions office, waiting room, views (golf course) and M & M’s!!!