how long = 1min 10sec to 1min 30sec. Keep an eye on the cpo as it should not show any visual melting or browning.
As for how hot I just set my oven as high as it will go which I think may be 550 or 450 something like that. Of course make sure the oven is preheated before you put the cp in. Only do this for metal cp's. Well it might work for wood but I doubt it as they reason this works so well is the metal heats up and stays heated which makes it pretty easy to remove the cpo. Have a heat safe place to set the cp when removed from the oven. have an oven mitt or whatever to grab the cp with as it will be hot and you don't want to burn yourself. Might also want a metal scraper or knife on hand to help get a corner up. One other note is if the cpo is really badly cracked and worn everywhere, this method doesn't help too much as the cpo will still come off in a million pieces and be a pain. Have a cleaner like goo gone on hand to do the finish clean up since some glue residue will be left behind on the cp.