I might be crazy or really dumb and also cheap but I'm attempting this goal with only 4 ovens I was able to build 4 on day one thanks to a good inventory of random parts and my awesome neighbors. I also cooked the 22 and 16 hour recipes ahead of time yesterday so now I'm only 6 hours away from completing part 2 and moving on to part 3. Now that I see I'm going to have to make so many more with only 4 days left I'm less optimistic but my determination to save as many coins as possible is keeping me from building more.
.... Sigh* I'll just have to wait and see and build some last minute if I have to...