How many you get depends on how long you are willing to wait and the size of your colony. I don't expect to "save" all of them. The most active (and hopefully the most healthy) roaches will get out of the frass onto the cartons or chunks of food sooner. When I am finished filtering the live ones out of the frass I pour it all into a trashbag, chill it in the fridge or outdoors (in winter!), then freeze it thoroughly before disposing.