Mmmm, I'm a little surprised that an ATMer hasn't suggested a simple modification for microwaves?
Not an Arduino or Raspberry Pi solution, but something similar?
Program a chip that accepts the time set by the user, and adjusts the speed of the turntable to return to it's starting position at the end of the cycle.
I'm sure it could be done?
Bojan, Alistairsam, and others, where are you?
Cheers
Chris