It depends on the model of case tumbler you are using. Some case tumblers can take only an hour to clean shell cases. Some can go as long as 3 hours to clean. Manufacturers usually put out the cleaning time of their case tumblers. Some case tumblers also have built-in timers to stop the cleaning process after a certain time automatically. I would recommend at least to let the cleaning process sit for 3 hours for your first time. After that, you can periodically check the cases in a certain period to determine how long it takes to complete a thorough cleaning.