What is it with all these recipes that specify, "Preheat the oven to..."? As far as I can tell, preheating is just a big waste of electricity or gas or whatever it is that powers your oven. I believe that recipe writers throw it into their recipes for two reasons. First, they want to sound professional. Second, they want to impose uniformity upon the mass of humanity. Because ovens will likely have an uneven warm up rate, it is impossible for them to calculate how long a dish will have to stay in an oven if it is NOT preheated. They do not have enough confidence in the individual. I have even less confidence in the average cookbook writer, as their time for baking never coincides with reality. It is nearly always short.
You will note that I do have confidence in you. Nowhere will you find a notation insisting on "preheat". Rather, I will specify a time for baking and hope you will check on the dish then. If it is not done check it periodically thereafter. Alternatively, you may use the following formula to calculate the time it takes for a dish to bake to finish: a2+b2=c. Where 'a' is temperature required; 'b' is the time specified; and 'c' is the square of the hypotenuse