The best thing to do about flushes, you will find that once your shrooms are fruiting some of them will be at a more advanced stage than others and you can leave a few days between harvesting allowing the less well developed ones to develop a bit more, but you will find that within a few days any that are developing will all be picked. Wash your hands, pick up the cake, pick off any aborts from underneath the cake. Take a sterile scalple blad...chop off any lumps and bumps (you will find that the cake grows these strange lumps of mycelium) scrape the whole surface area of the cake so that it is taken down to fresh substrate...(at this point you can use Hippies Dunking Tek (link in the links section)which is basically submerging your cakes in water for 24hrs to rehydrate the cakes...or just place them directly on the surface of the perlite to soak up some moisture)
The cakes can then be put back in the terrarium and left to their own devices to recover and wait for the next flush. Some cakes may manage 2 flushes others 3-4. You will soon see when a cake has come to the end of its natural life...it may turn blue or start contaminating.