Five day for Panacur (Fenbendazole)
It is a safe as houses- you have to actually drown the horse in it to do any harm!!
It is also safe for foals, from ten days.
Ivermectin I use for foals from six weeks on.
I do the Fenbendazole five day twice a year, in Autumn and in Spring, it clears out encysted small redworms, and they are the worms that will REALLY do some damage.