You can definitely overdo it with certain kinds. It depends on the brand. I would read the instructions. If it's a liquid, I would put it around the coronet band and let it drip down. Doing it twice a week seems reasonable. :) At least until the horse's hooves get hydrated and healthy again, and then I would tone it down a little and use it only when he needs it.
I use Hoof Savor, which is more like a paste. You can put it on the whole hoof and especially around the heel and coronet band.