I bought an outlet timer at Wal-Mart. I set it for 3 hours, and let it run before I go to bed. Gets things nice and clean.
I've found walnut shells will scour out the dirt and grime, but corncob with non-ammonia brass polish gives that bright "new brass" shine. Possibly overkill, but presently I use both media sequentially, for a total of 6 hours of tumbling/load. It did put a good finish on some ugly-as-sin Indian surplus 7.62 NATO brass.
This all happens in down time, and I'm not producing at the rate some folks here do. Were I in a serious production mode, I'd just use the walnut shells and not worry about "pretty."