i turn on the oven right before grabbing the pizza. by the time the pizza is unwrapped, and doctored-up if i'm gonna add something, the oven is 'warm enough'. if a brand of pizza routinely gets done 'too fast' on the bottom, i put a cookie sheet on the other rack underneath the pizza with about 4 minutes left. if i add lots of cheese or other stuff to the top, i might pop on the broiler for the last minute. only need 325F regardless of what the box says, and less time than it says, and the rack the pizza is on has to go one notch higher in the oven than for everything else. my oven is stupid. it only took like 10 years of trial-and-error to figure out the best way to make a frozen pizza in it, and step 1 is 'ignore the instructions'.