Hi Patton,
I'm not positive but I think the vibratory tumbler will cut faster but with the low price on the Harbor Freight rotary tumbler it would be interesting to give it a try.
I just experiment with the time, taking a look at the parts every few hours at the beginning to see if the parts are getting a uniform clean appearance. Once it gets to that appearance, I take the parts out. Some parts or certain areas on the parts don't clean up completely and I finish them up quickly with glass bead or wire wheel.
I have found a small amount of metal filings in the sand media (when using a magnet to find little parts that pass through the sifting basket) but haven't noticed parts with excessive wear. The recessed and inside areas, like the roots of the threads are the slowest to get cleaned up so I think it would take many days of tumbling to cause wear problems. The walnut shell media seems to just polish, not remove metal, so the longer time doesn't seem to harm the parts at all.
Cheers,
John