The problem could be the control panel (keypad) or the electronic control (timer).
The usual way to troubleshoot this is to check the keypad outputs and if they are OK then replace the timer. But I cannot find info on the actual keypad outputs so unless you have some experience troubleshooting keypads this will not be an option.
You could try the following.
Connector Cleaning / Checking
Unplug the unit
Open it up
Remove the ribbon cable from the keypad to the control board at the control board.
Clean the edge connector. Use electronics contact cleaner or isopropyl alcohol.
If it is the type where there is not a connector just the insulation is removed, it can be cleaned with a pencil eraser. Do not use an ink eraser as it is too abrasive.
Check the tracks in the ribbon cable for hairline cracks. A magnifying glass helps here.
Would not hurt to clean the connector on the board. Use electronics contact cleaner or isopropyl alcohol and a tooth brush. Be gentle and do not reconnect till all the solvent evaporates.
Reconnect everything and give it a try.
If this does nothing then pretty well all you can do is take a gamble on one of the parts.