How do I get my parents to let me stay out later tonight?

I'm 17, a senior in high school. My curfew on weeknights is 10:30, and midnight on weekends. This usually isn't really a big deal, except now I have an internship with this company that puts on concerts. As a part of my internship, they want me to p out flyers after a show tonight at 11:30, even if it's only for 15 minutes or so. I'd like to go into this business when I'm older and doing this means more to me than anything in the world. The problem is that my parents are the stubborn, no-negotiation types. What can I say so that they'll let me stay out until 12? My grades are fine, and it's the second semester of senior year...really now...