I have always put the meat on as son as I dump my lit coals on the unlit. Thought being that if I wait to get up to temp, then open the smoker and add 7lb, 8lb,10lb of cold meat (depending on what you're smoking) it's just gonna throw the temp out of whack anyway. I'm a bit different as I like to use about 1/2 a chimney of lit coals to get the smoker up to temp, not 10 or 12 coals. I dump the lit coals on top of unlit and leave all 3 vents wide open until I'm about 20° below my target temp. At that point I close 2 of the 3 bottom vents all the way, and the 3rd vent I close about 90%. For me , on my smoker, this kills the rapid temp increase and levels the temp almost exactly where I want it. From the time I dump the lit coals, put my meat on the smoker, and get the smoker put together, to the time I hit my target temp of +\-265° it usually takes about 30 minutes....
Hope this helps,
Tim