Here's something that suprised me. I tried to start a 0.20 engine while holding it in my hand once (only put a few drops in carb so I wasn't planning on running for any length of time). Flipped it over and after a quick blip on the throttle, the engine was VERY hot. I got curious and while my TT .46 pro was cold at the field I started it and immediately touched the head. Within one second it was hot. These things don't take long to 'warm up'. The main thing is to have the engine inside the house before you start it so that it's doesn't get down to below freezing temps. If the planes inside at a nice 72°f then you go outside and start it the ONLY difference is that the intake air is cooler (okay ambient is too so cooling will be better but that just makes for a safer breakin). Don't sweat it, but then again dont leave your engine in the freeze for 3 hours then fire it right up as the metal has different expansion/contraction coeffecients.

- Joe