It's October 3rd.

Because on October 3rd Aaron Samuels asked Cady what day it was and she told him it was October 3rd.

to metalman: https://pbs.twimg.com/media/BVqwfUpCMAAFmZm.jpg

I see, I haven't seen the movie except small bits so I had no idea thanks for explaining

Now it's 5 October o_O

I was waiting for this