I just matched this past spring - it is unfortunately INCREDIBLY common these days for programs to send out more invitations than spots, across multiple specialties. I forget if it was from ERAS or the NRMP, but we got a few emails throughout interview season with "reminders" of the professionalism guidelines for the match, and this was one of the policies on the programs' end that they reiterated a few times. If you don't respond within like an hour (and often less) of getting your interview invite, there's a decent chance you'd be out of luck for getting an interview spot at all, let alone one that worked with your schedule.
OP: I would hold off for the rest of this week and see if the program coordinator gets back to you. You said it was for "confirmation of dates" - if you selected a date and are just waiting to hear back to confirm, I'd plan on getting that date. If you don't hear anything, call her this coming Monday to confirm the date and also come up with some other relevant question to ask about like local hotels they recommend or something. Tenk is right that coming off poorly to the program coordinator can royally screw you over at a program - continue to express a polite amount of interest but be very careful not to be overly pushy. And if you don't hear back...so be it. I had a few programs that I interviewed at that had some scheduling issues like this, and when I went in person I found that these organization issues tended to be present throughout the program. If they can't get it together for recruitment, when they're really working to put their best foot forward, then they probably won't get it together for the current residents either.
