I'm in with those who use a minimal warm-up. Really just enough to get warm air through the horn and blood flowing through the lips. If I think I need more than that I'll make sure to arrive early and blow in my car (usually on my pocket trumpet) but even then it's only for 5 minutes. A guy (nont a pro) I used to regularly play a church job with would ALWAYS ask the music director where he should go to warm up, and then disappear for 10 minutes while everyone else talked about the performance, changes, etc. The director eventually stopped calling him.