If you own a timing light, the engine should be timed with the bike warmed up and running steady at the RPM specified as full advance in your manual. Engines spend very little of their total running time at idle, hence timing dynamically using the static timing mark makes little sense.
If you have a concern that the mechanical advance mechanism is not working properly, then watching the full advance come into the window as you smoothly increase RPM will help make a determination concerning proper function of the bob weights.
So, yes, start the bike, verify full advance at a steady RPM, and if required, stop the engine, correct the timing, start the bike, and retest. Fortunately, the Dyna S was specifically designed for lazy lads. You only need to set the timing once in the life of the machine.
IMHO Gunning an engine never makes sense as a normal operation procedure unless the bike does not have a idle stop, a properly set idle circuit, or the operator has a difficult time picking up women.
Ciao,
Dick