Leaving early at a Bar Mitzvah?

This weekend is my friend's bar mitzvah, and it is also the weekend I have my play performances. I have to be at the theater at 12:30, and I think that's the time my friend's service ends, but since I need to BE THERE by 12:30, I would have to leave around 12:10. Do you think I could leave during the service if I had to? Or is it rude, and would it be best not to go to the service at all? Thanks! Just wondering.