My interview day ended around 5.20( they were running a bit late that day). My return flight was the following morning (Saturday) and it took me a good 1.5 hours to get from Pontiac to DTW. You should be fine but I have no idea about evening traffic on a weekday. So, I would err on the side of caution and leave early if they are running a bit late ( or skip the tour all together). But that's just me, I'm paranoid when it comes to flights
P.S. The tour is awesome btw. The campus is beautiful and the anatomy lab is sparkling clean!
P.P.S. It's quite possible I didn't help you at all
😳