Yeah, I think it's good to look into this area but there are a few negative reactions to altering the timing in the motor for tanks. They do turn both directions, unlike a slot car motor. I know it's only a few degrees as they are 0 timed.
They do produce motors for aircraft that have the timing advanced... not so good to use in RC tanks.
I would look more into the gearing, pinion gear change or even using a motor with a different RPM rating that would in effect make the motor slower or faster, depending.
Jeff