Thank you your question.
I have checked the model number that you have submitted. You are right the knob should unscrew from the timer shaft. Push the timer knob in and turn the knob counter clockwise. The knob should come off. I have seen when the time is internally broken and the timer shaft spins freely in both directions. In this case, you can try to hold the shaft from the backside with a pair of pliers. I have also had to dismantle the timer to hold the shaft to unscrew the knob.
I have sent you the instructions for opening the console on your washer.
If you need further assistance, please reply with more details below.
Thank you for using Manage my life.
Here is a link to order any parts you need.
Sears Parts Direct
If you do not feel confident repairing this problem yourself, then you can have it repaired at your home by a Sears technician. Here is a link for the website:
Sears Home Services