That wasn't my experience...I had a duplicate key cut right after I bought my car, and the dealer parts counter man told me to go out to my car, start it with the old key, allow it to run for at least 30 seconds with the new key in the car, turn the ignition off, then insert the new key and start the engine with the new key within 10 seconds of removing the old key.

The most painful part of the whole experience was paying 46 bucks for the key.