I hate to tell you and burst your frugal bubbles here, but this only works during the winter and it has to do with one of Newton's Laws:
All energy is conserved, neither created or destroyed.
When you heat the oven, you heat the air inside, plus the metal, which is then contained in insulation. When you turn it off, very slowly, the heat dissipates into the surroundings.
So. . .your heater. to keep your house at 65 degrees. actually had to work extra to keep the house warm because you weren't running the oven for that 5 minutes.
Now, in the summer, where you have the air conditioner working against the oven, this is a smart thing to do. By all means, turn the oven off as soon as possible.
See? I can be a frugal nerd too.
But here's a tip on the same note: Wait til your bath water goes cold in the winter before you drain it. The heat will radiate into the surroundings and make your heater work a tiny bit less. We usually wait a day before we drain dirty bath water.
In the summer. . .let the hot water drain as quickly as you can. Try not to do baths in the summer (hard for kids. . .so just drain it quick).