I agree. I've asked drivers to leave early many times at DTW and elsewhere and never gotten the slightest indication that they expected something in return. Part of what you pay for when you rent from Hertz is classy treatment, which should include a bit of flexibility once in a while when a customer needs help that can easily be provided (such as doing the bus run a couple minutes early). Even if you don't know the driver's name the Hertz DTW people will be able to figure it out.