In the scene right before the Mitch-A-Palooza, you see a sign on a tree that says "Mitch-A-Palooza" with a picture of Mitch's face and it says Thursday Night 8:00pm. Later in the movie, during the party "Frank the Tank" (Will Ferrell) walks by college students and ask him if he wants some beer from the beer bong. He says "No, i have too much stuff i have to do tomorrow" and the kids ask what and he says "It's a pretty nice little Saturday actually." If the party was on a Thursday, why would tomorrow be Saturday? And also the next morning, Mitch finds himself in bed with a girl. He goes to work later that day and finds out that's his Boss's daughter. Again, it's the next day, Friday, not Saturday.