@mistyk,
I'd be more concerned about him stepping out 3x/week until 3 AM. The app may or may not be related but the big problem is him going out with the guys all the time.
At best it make him look inconsiderate and immature, and it may point to alcoholism or a drug addiction. At worst, well, you know what the worst of it is.
So instead of confronting him about his phone, why aren't you talking to him about his social habits?