The shorter the race, the longer the warm-up. Many on here may have very indepth warmups, but for me its just about getting the body going. I don't even want to break a sweat. I find i have no better performances following a simple warmup as compared to a complex one. For a short TT (less than 10 miles) i typically get on the bike 1 hour before my start time. 20 minutes of easy spinning, then a few one minute efforts around threshold (maybe a little higher, closer to race pace)with 2-3 minutes in between each (10 minutes total). 10 more minutes of spinning. 5 minutes at or just below threshold, and then spin easy for 5 minutes or so. Get off the bike 10 minutes before the start, slam a gel, grab some water, and off you go. It is good to get all of the energy systems up and running, lactate clearing, etc, but it doesn't take much. You want your system ready to go from the gun and with 5 miles you don't have any room to take off easy and build up to your goal pace. Warmup is huge for such a short race. I'm sure there will be lots of opinons on this, so take all you learn, think about each of the posts, and build your own warm up routine. Also a fan blowing on you as you warm up in the shade, and a wet tshirt if it's hot are good to keep you from overheating and getting dehydrated. Also drink during the warmup.