The other technicians are probably correct about replacing the timer
Before you do that, try this just for the heck of it...
First, be sure the pointer knob or indicator knob is not binding up against
the console panel (from underneath) I have seen these knobs get pushed back very snugly against the panel and the friction this causes is just
enough to stall out the timer drive motor, when the added torque is needed to end the cycle and reset the "start knob" (pop it back out).
Two, remove the timer and place a drop or two of a plastic safe silicon lubricant
at the spots I have indicated in the pictures...
If this works... Oh happy day,,,GREAT!!! if not just replace the timer!
peace, and good luck