400 miles isn't that far. It's approximately the distance from Minneapolis, MN to Milwaukee, WI, which is a trip that I've done nonstop. It takes around 5.5 hours, which isn't too bad. Start around noon and arrive just a little before dinner.
Minneapolis to Chicago is a bit longer (a little over 400 miles), and takes about 6 hours. For that I'd probably need to stop somewhere to eat.
Assuming you pee at the origin and the destination, and it's freeway driving, that's two rounds of three hours between the bathroom. As long as the weather is nice, and you don't overhydrate, that doesn't seem unreasonable.
