I have done several hundred turkeys this way, and to do it overnight would NOT be that great an idea. No matter how low and slow you'd go, you would still come up with overcooked, dry breast turkeys. Altoshams are great for steamships, or slow cooking other proteins, but not turkey.
For our Thanksgiving buffets or Mother's Day, Easter, etc.....I'd start them at 235-240 around 3:00 am- 4:00 am. By 11:00am they are pretty well done the way you'd want them.
I would be careful not to go any lower then that as the inside of the bird would be in the "danger zone" too long.
I agree with Chefross. Never had a problem with Alto or any other brand auto slow cook oven. Large cuts of beef, pork and poultry usually come out best. 240 is highest temp I have ever used on anything.