Don't change the date. As others have said, it doesn't look good to change your date without having a good reason (even "I have an exam that day" apparently isn't viewed as a "good reason" by many schools). Not to mention that with an interview this early you are definitely among the first group of interviewees which is an enviable position. Getting started now will also give you practice for later interviews that may you care more about. If you don't care about any of that, then consider that you'll likely have more interviews coming down the pipe and the last thing you want is to have put yourself in a position where you have multiple interviews in a single busy week when you could have had something more manageable. Finally, if you interview well and get an acceptance soon, that's going to be a massive stress reliever for the rest of the cycle.
BTW, what school is this? I wasn't aware any MD programs were doing interviews yet, although now that I think about it I guess I'm actually thinking of MSTP. Still, August 1st seems super early.
