your asking about stopping them at a certain time according to the dropping of flights but you must also be aware of other conditions: when they're bald around the head & when the covert feathers on the wing fall (best described when the bars of blues start to fall), in this condition they'll feel knotty. Any rain about they'll get saturated. Once through the body moult you can bring them out again and get another couple of races out of them but you have to be wary of the dropping of the last two flights, if the second from last is just pushing through leave them at home but once its grown an inch & half you can race them and they'll be in perfect condition. Once the second from last is 2/3rds grown thats its racing finished for the year.