No, use only needs to be continued as long as there are androgens in the system that are capable of being reduced to DHT. Along the same lines as anti-aromatose drugs. They only need to be taken when there are high levels or a hormone in the system that is prone to conversion - and needs to be stopped.
Another, and probably better, alternative for stopping 5-ar from occuring would be dutasteride. I don't have a lot of first hand knowledge in this area, as I'm blessed to not have the need for it. But from what I've gathered, you'd be best off using only minimal amounts of a systematic 5-ar drug (if at all) - and concentrating on topical solutions. Reasons being DHT has many important functions in the body and shouldn't be diminished too much, as well as sides from the systematic drugs.