Which visit are you going to go on? If you haven't made a decision yet, I can offer some advice! I know many of the professors and their grad students will be at the APS March Meeting during the March 2 weekend, so if you have several profs you want to talk to, go to the March 30! Hope to see you there :-)
Just got my acceptance email from Michigan MS&E yesterday! Looks like the visitation weekends for engineers are either March 8-11 or March 22-25, who is going when?