Yes if you want to harvest plutonium for warheads, you have to take the fuel out the of the reactor very frequently, which reduces the efficiency of the reactor. Since the fast breeder reactors are still under development it should run undisturbed for a long time, may be continuously for four to five years. If it is disturbed frequently, then the developmental program will hinder, and it will be delayed for many decades. But before, since India has many conventinal reactors, and they were not under anyone's surveillance, it was possible to harvest plutonium. The scheduling might have been done in such a way that not all of them are running simultaneously and some of them are under maintainance. Such information are available in plenty in the internet.
