The flipside to summer visits- the faculty is around; grad students are around; we had a few serendipitous conversations with professors (standing on line for ice cream on a hot day…) which were really tremendous opportunities. They’re at work but more relaxed since they aren’t running from a 1 pm lecture to a 3 pm faculty meeting…
We found the more relaxed campus environment very helpful if there are specific programs or departments your kid is interested in. And we found Admissions very helpful in setting up scheduled meetings with specific faculty… in addition to “bumping in” to professors who were always happy to be helpful.