Well, the sun goes from east to west, so the line of day switch would also go from east to west. Some time ago, hh opened his account, and that time was Dec 18th for some of us and 19th for others. It was close to 12 pm for hh, his timezone is UTC+2. We need someone close to that time to find out the details of when the site was created, assuming hh is the first account. This may not have resolution of more than an hour. Or we can wait for hh to wake up.
edit: Timezones change, Poland is UTC:+2 right now, Turkey and Finland are UTC:+3. I had a 1 hour difference with Nie. Hhyyrylainen opened his account in December 19th, between 12 pm and 1 am. It was still December 18th for people living further to the west. 18 hours later(Dec 19, '17 5:47 PM, UTC:+3), he posted this:
From this, we can learn that Hhyyrylainen goes to sleep after midnight and wakes up before 5 pm.
I should find a better way to spend time.