The 7th is a transition day and the 8th and 9th are the first couple days of classes. If you are interested in seeing more than just the view from the chapel wall and the visitor's center, there might be a friendly cadet on here willing to show you around a bit. Otherwise, I would say it doesn't really matter which day you visit. There may be a noon meal formation on Friday though, if you are interested in seeing that. Not sure how much the schedule of calls has changed in a year so hopefully a current cadet will get some time to chime in.