Whatever it says you can double. But after that, their effectiveness is probably zilch. Pretty good, assuming you've done it correctly. Exactly HOW and WHY it works on the roaches is gruesome. Roaches are cannibalistic and will readily eat other dead or dying roaches.
Roaches are also coprophagous , which means they eat each others excrement.
In fact, new little roaches do this soon after birth, and MUST do it to survive. When the bait poisons and kills a roach, that roach, and his excrement, becomes poison for other roaches, that, in turn, become poison for still more roaches. This product is best used when you discover the problem. Otherwise, you'll have to change them, on a routine basis, for them to remain effective and active. This is false economy, so don't waste your money.