Once you observe the timer has stopped moving. Then verify the timer motor is receiving voltage still at the same time. It then is probably the timer sticking. You should be able to detect the actual motor wires and terminals.

The dryer is old enough an appliance service place might have a good used timer. Some areas have piles of scrapped appliances where one might find the part for free or almost free.

I went to purchase some common parts for two of the wifes stoves awhile back. The current prices floored me as we used to sell those parts. No wonder people just replace appliances when needing repair. Parts prices today almost make them throwaways. The wives dishwasher at home is down at three years of age. She is at the cottage for the summer so it can wait for me to have a look at it.

More on a point of principal I found some discarded units easily and got the parts from them. I asked permission to remove the parts and the guy said they are yours.