I don't know that I've ever had two races three hours apart. I'd definitely eat and drink in between. Maybe even take a nap and stretch as well.

During our Tuesday night race series, which is on an oval car race track, I race back to back (4/5 first then 3/4). During the 10 minutes in between, I try to take a gel and drink - though this is often difficult due to the fact that I am also trying to recover from the final sprint. And as others have said, the first 10 minutes or so of the second race are pretty tough, but once I get settled, I tend to do all right.