If these are summer visits without an interview, it is technically possible to do 3 a day if the stars align but I would aim for 2. You may find, though, that when you schedule, they offer you an interview (or more than what you are seeing from the website).
Summer visits don’t allow you to see who the students are, which is really important. But you are more likely to find the folks you meet are less rushed and can make more time for you, so it’d be a bit of a pity to have to run because of scheduling.
We found when doing college tours that getting from place to place in an unfamiliar area, finding the right buildings, and keeping everyone fed took a bit more time than the times on google maps.
If you are doing drive bys and aren’t meeting with anyone – in other words, just looking at a campus, sure - doable but not so valuable.
Pretty sure @Calliemomofgirls did summer visits from the other side of the country and would have good input.
Definitely have a means to record reactions as you are leaving each school as they are likely to blur together!