I've made lasagne lots of time and most always have to check a cookbook to verify the baking time. Thus, I checked a very reliable source, my Better Homes and Garden cookbook. They say "Bake in 375 oven for 30 to 35 minutes or till heated through. Let stand 10 minutes". Since I usually will prepare the lasagne baking dish and refrigerate prior to baking, the time must be extended to really heat through. I will poke a small knife in the center of the baking dish and make sure it's hot, could take up to an hour. So, it's best to allow extra time. Since all the ingredients are already cooked, you are basically just melting the cheese and reheating the sauce and lasagne noodles. Also, making it ahead of time allows some of the flavors of the sause to sneak into the noodles. Additionally, by making it ahead, all the mess can be cleaned up prior and it's just a matter of salad and bread to make while the lasagne bakes. I really serve this often for company, as little after dinner clean up due to earlier preparations. Leftovers are always great, just nuke and serve.