Hi...
I have tried walnut, corncob and washing brass in lemishine, Dawn and hot water.
Washing the brass and drying takes a lot of hands on effort and time, corncob in my opinion doesn't work as well as walnut.
I run my tumblers for about 3-4 hours...generally separate the brass by caliber before tumbling.
I clean rifle primer pockets after depriming and resizing. Handgun brass ...sometimes I clean the primer pockets after depriming and resizing, sometimes I don't. Don't think it makes any difference to be honest. I can't remember the last time I cleaned primer pockets on .357Mag, .45ACP, 9mm, 10mm or .40S&W. They all get reloaded on my Hornady LnL progressive presses. I never deprime before tumbling.
All of my other revolver reloading is done on my RockChucker and O clean the primer pockets about every two or three times they are reloaded. Usually do somewhere between 250-500 in each caliber from .38Spl, .41Mag, .44Mag, .44Spl, .45Colt and .45AutoRim. I also keep a batch of 500 cases in .357Mag for heavy loads with jacketed bullets that get the primer pockets cleaned every few loadings.