question- i have a large oven that takes a while to heat up can i coat my part with the oven off and then put in my part and then turn oven on and let it sit in there for the pry 30 minutes or so that it takes to heat up then bake it the 20 min once its at 400? or do i need to preheat no matter what, reason im asking is my oven doesnt have one large door to get things in and out so when im doin large items its a real hassle unless the oven is off or i finish with multiple burns on me! thanx in advance.