I would say that the frequency of shaving is less dependant on the actual length of whiskers (although that can affect the quality/closeness of the shave) but whether or not your face can handle it.

I can feel stubble growing back fairly quickly even after the closest of shave, and could technically be possible to shave every day easily based on whisker length alone. But my skin can't take the rigours of daily shaving, so it's every other day or so for me.