No plan exactly. Usually at least a few months until the plants are established pretty well. It was usually my work schedule and traveling, combined with some laziness, that determined when I stopped adding CO2. I'd still do half doses of Flourish once every couple of weeks or at every water change, if I remembered.
I think it's important not to mess with the tanks too much once they have established themselves. Let them maintain themselves. If you try to control it too much, you run into issues.
Just keep an eye on it in the beginning and keep it heavily planted and you should be good. When parameters level out, it coasts along on its own.