Day1 is the day it started. Which is for this one, today.
From the front page of that gacha, hit right. That will show you a SSR Hime which has the Rate Up. That way you can tell which day it is. There's also the button which shows you the rates (though they aren't very detailed , SSR Hime is ~1.8% and SSR Eidolon is ~1.2%, but that page only reports 3% SSR).