Yeah if it's somewhere you really wanna go, try and interview somewhere else first. This will help take the edge off and kind of let you experience the process before you really wanna make a good impression. If you're gonna blow an interview, it'll likely be the first one you attend.
I still don't see what the two interview dates has to do with your original question though. If you're talking about interviews a couple of weeks apart, it's no big deal. If a school has a spot open this week and a spot open in May with nothing in between, it matters. Although that's obviously not the case.