When is DG formal?

Hey girlies a little help here. I don’t go to UF but my boyfriend does and weirdly brought up the fact that will be pulling an all nighter in the library for a big exam on a specific night and planning on locking his phone in his apartment that night. It just felt weird and suspicious and my gut feeling is that it has something to do with a girl. Since it’s that time of year I think he’s going to his female “friend’s” formal. He snapchats her all the time but I have never met her when I’ve visited. A quick Instagram search of her name showed me she was in DG. I have a feeling this girl doesn’t knows I exist so no hate on her or anything… but just looking to see if the sorority’s formal aligns with the night he said he has to study