It does it on UK time which might cause a little confusion for some people.
It ignores the time aspect of it, and just focuses on the day/month/year.
IE, you visit on 20th Nov, your counter is set to 1
you visit on the 21st Nov, your counter is 2
you visit on the 23rd Nov, counter is reset.
It's done on UK date. If you visit the same time every day it shouldn't matter and the counter should still go up.