Isoort is basically a natural HC (hydrocortisone) replacement, it was banned by the FDA for this reason. Yes it can work that quickly as thats what HC is for, instant cortisol replacement. Its around 2.5mg of cortisol.
Its no longer available, so getting hooked on something that can no longer be bought or in fact made might be a bit of a drastic move, unless your ND has a huge supply.