I also do a full warm up and run the closer before actually trying to use the tuner. I usually start with F around the room and see what the average is, and give them the "trumpets push half inch in" instructions before going down the line. This will save you some time. I do one or two sections then play for a few more minutes, do one or two more...so that way the instruments don't get cold sitting there.
Also, on field warm-ups are really smart when it's cold (especially if you're sitting at the gate for 10 minutes before you take the field). Just block up to the visitors bleachers or the scoreboard and play through a short part of the warm up once or twice to get the horns back to temperature.