I do enjoy shutting the engine down on my personal Challenger II. The engine does cool off rather quickly. In my own experience, I believe that the cooling of a mere 5 minutes of gliding is somewhat comparable to letting the engine sit for an hour or better on the ground. On the ground, the engine takes longer to cool because the heat is merely radiating away. In the air, the flow of air through and around the engine causes it to cool down at a faster rate. If I choose to restart in the air, I have one hand "at the ready" on the enricher (choke) lever as I turn the ignition switch to the start position. If the engine doesn't fire away after a few spins, I feed in the choke and it comes to life like the first start of the day. When I do shut the engine down in flight, I only do so when I am in a position to safely make it to a suitable landing spot. I treat the plane like a glider that MIGHT possibly have the ability to restart in flight. Prior to shutting the engine down, I sloooowly decrease the throttle to idle and leave it there for at least 30 seconds or so prior to shutdown. On restart, with sufficient altitude, I slowly feed the throttle back in and then resume normal flying.