You should have a look at it... I did very simple repairs to my dishwasher timer and to my dryer timer recently and both were successful and didn't require any parts replacements...
If it's the same timer as in my 1969 Custom Imperial, the two tabs on the motor gear might be broken. I was able to fix mine with Loctite 495 glue but that's a temporary fix! I just ordered a new one on eBay...
But first remove yours (it's located below the dishwasher, remove the lower panels, then remove the two screws that hold the braket to the right "leg" of the dishwasher, then remove the two screws that hold the timer to the bracket (those on each side of the timer manual advance shaft) after that, remove the two screws that hold the round timer motor (not the rectangular rapid advance motor), disconnect the two motor wires on the timer plug them on a 110 volt wire to see what happens. If the gear doesn't turn, it's very likely to have the same problem as mine had and the one shown on the links above. Then follow the procedures on Davesrepair website...
I just ran mine for a complete cycle and eveything works now!