The kitchen timer should have no effect on the oven operation, it's just timer.
Dual oven relay control board 316443936 receives signals from the main oven control board. The relay control board operates relays to regulate the oven elements.
The main control panel (5304507689) manages the functions of the wall oven such as heating and temperature.
You might have an issue with the relays on the relay control board, it may be an issue with the main control board, the control board touchpad (139038845), or it may be an issue with a wiring harness. Another issue that can cause an oven to turn off by itself is a faulty thermostat. As the oven gets to the temperature you've set for it, it needs a functioning thermostat or sensor to let it know it has reached the right temperature. If the thermostat is broken, the oven might shut off too soon, thinking it is already at the desired temperature.
You can find parts and diagrams on Sears PartsDirect: searspartsdirect.com/model/1uvknt8vjg-000582/kenmore-79049533316-electric-wall-oven-parts
If you have an error code: searspartsdirect.com/diy/error-codes/wall-oven-repair/1234576-1235921/kenmore-self-cleaning-wall-oven%20/0582
If you don't have an error code, I would suggest calling Sears Home Services at 1-800-4-MY-HOME for repair so that you don't go on a while goose chase replacing parts that don't solve the issue.