Open Reg is the same weekend as the clock changes (fall back one hour). That doesn't really affect us in the US/North America, because the change technically occurs at 2:00 AM on that Sunday, but I wonder if/how that affects those internationally in other time zones.
Side Note:
My first open reg was 2015. I didn't read anything on the site. I just followed the instructions that came in the email. I'm on the east coast. When they said the waiting room would open at 8:00 AM pacific, for some reason, in my head I thought that meant 5:00 AM my time. Instead of adding 3 hours, I subtracted. Sure enough, I was up at 5:00 AM ready to log on. And sure enough, I got the notification I was early.

. If there had been other people around, I would have been embarrassed. I mean, come on, I'm an adult WHO WORKS IN IT, and... I WAS A MATH MAJOR. Go figure.

Oh well, that was a better mistake than missing open reg altogether.