I think gameday for Europeans is the time most users are online, I usually see 2000+ around those times. But it's also important to take into account when the people online have money; so I'd time it so your player's deadline is right after the games. Most European countries have GMT+1 or CET, which is 6 hours earlier than US Eastern. The games end around 8:30 PM here, so it's 2:30 PM Eastern. If you put your player's deadline at 3 PM ET, most people will be online with money.