WDstarting problem

I think the timing on my WD is too far advanced as it won't start hot. How far would I rotate the distributor to retard it, and in which direction? Would I do it with the engine running?

While it"s running, loosen the bolts and turn the distributor each way until you find the sweet spot. You"ll hear the engine sound change. Find the mid point.

As JM says. I time engines all the time by ear. You listen to the running and find that spot where you have good power but also easy starting. But that said before you set the timing double check your points and make sure they are set to the correct 0.020 setting. If the points have slipped or are old that will cause the timing to be off also

Make sure that the rotor is lined up with # 1 spark plug wire and it will start , then set the timing dead on

What am I listening for...the fastest speed, smoothest running, how do I know when I've got it right?

You want the highest RPM but you also want it to start easy. If you advance it to far you will have good power but will be hard to start when warm. The way I do it is take a wrench with me and take it out for a drive and adjust till I fine that sweet spot but I have also been doing that for decades

Most WD's had magnetos. The impulse action automatically gave you retarded timing for starting, and advanced timing for running.
If you have a distributor, you have to count on the advance mechanism to change timing. They have been known to rust/set-up. Hopefully you can grab the rotor/cam part and it will turn a little free of the main dist. shaft. There was originally a little felt in the hollow shaft, under the rotor, to lube between the shafts.
The dist. turns clockwise, so turning the dist. housing to the left, or against the rotation, advances timing. Timing advanced too far may run a little rough, kick back on starting, etc. Timing retarded too far makes an engine labor. lack power, run hot, etc.
In the absence of experience in timing by ear, you may want to use a timing light. The marks (TDC, or 0 degrees, and advanced, 25 or so degrees) are on the flywheel, accessible through the hole in the bottom of the housing.
With a timing light checking the advance is easy as you should be able to set high speed on the advance mark, then as you slow the engine down, the timing should move towards the TDC mark. Ideally, the engine will crank, start, and SLOW idle at about TDC, or 0 degrees, but in reality most of these old advances don't work as good as new, but good enough.