When I CPOP, I preheat my oven to 170, then turn it off. I open the door a little and after 10 - 15 minutes or so, I put my soap in the oven, close the door and leave it to sit. If I'm soaping during the day, I let it sit for about 2 hours, remove it, cover with a towel and put it in an out of the way place. If I'm soaping at night, I just leave it in the oven til morning.
I always thought that the purpose of CPOP was to "jump start" gel. So to me leaving the soap in an oven with the heat on never made sense.
Lately, I've just been setting my soap batter filled mold on a heating pad and covering with an old baby blanket. The heating pad has a safety feature that shuts it off after an hour and I've found that by that time gel has been jump started. Easy-Peezy and you don't have to worry about preheating the oven; when to take it out, etc. etc.