I did the something similar. I got the email but was traveling so I couldn’t get online to schedule it and ended up with October 4th for my interview date. Then some stuff came up so I had to reschedule it, which is as simple as going back to the portal and clicking the link that says reschedule, and I was actually able to get an earlier date that wasn’t available when I first scheduled it. I’m guessing somebody had to cancel/reschedule and there were a few earlier dates with 1 available slot. All that is to say, if you’re concerned about your date maybe try checking to reschedule periodically and you might find an earlier date with a slot by chance.