My normal loading procedure entails throwing the cases into the tumbler after belling the mouths. When I'm loading auto cases, there may be 200 to as many as 500 cases at a time...I shoot competition, usually, but not limited to Steel Challenge. When I go to a two-day event, I need at least 600 rounds, and I don't use a progressive. I DO use a progressive for my trap-shooting ammo, tho'.
Anyway, after loading a hundred or so, I throw them into the tumbler to wipe off the grease. I'm loading lead bullets, so some of the lube gets on the cases, and I don't like the cases to be stickey from the sand and dirt that is on the ranges I use. I keep cleaning the guns, but they get gummed up anyway. I'm just trying to keep it to a minimum.
They stay in the tumbler for at least an hour, or slightly longer. I don't see how there can be any harm done, compared to the hours/days the powder is in a truck going across country, then moved by forklift/palleting around a warehouse before it gets to me.