Thank you! The problem with your plan is that electric roasters generally cook quite a bit faster than regular ovens, not more slowly. There are other problems, too.

What the government's food safety people are concerned about is whatever portion of your turkey stays below 140°F (60°C) for whatever period of time. Their goal is that it be no longer than 2 hours. If you had a way to get the entire turkey to 140°F quickly, they would let you take as long as you like to get the turkey finished (to 165°F (105°C) in the thickest part of the thigh). The problem is, of course, that you can't get the turkey to 140°F quickly (other than deep frying), and then it doesn't take all that long for the last 25°F.

If you set a conventional oven to 200°F or even 250°F (93°C or 121°C), portions of your turkey – depending on its size – would spend hours and hours below 140°F. On top of that, you want to use a roaster, which is likely to cut 25% or so off your cooking time. You're going to need an awfully short night!

We understand you have a plan and it hurts us to deny you, but you did use the word "safe" in your question, and we're going to have to side with the government on this one (325°F (163°C) is the lowest oven temperature setting they allow for cooking a turkey).

Are there people who do what you suggest? Quite likely. Are they taking risks? They are.

While we use our every breath begging people to get a reliable meat thermometer, we're just going to suggest you get (or remember to set) an alarm clock.