I have a frustrating problem, when I don't take my time to warm-up properly I'm not able to play as good as I do other times. Sometimes I can't even hit some notes (in middle range), having the feeling that my lips don't want to co-operate/vibrate properly, which is ridicolous. So when I go to the lessons from my teacher I always play worse then I'm able to, and make less progress due to that. At home I take 10-15minutes warm-up time. But in the lessons it's maybe 5min, probably less... My teacher says that I just have to warmup less at home, so that I'll be less dependent on it. For me, 10-15min of warm-up seems normal and needed to me, I just want some opinions on this. To be honest, I don't want to cut in my warm-up... Regards!