I'm making a fondant shoe for a birthday cake and it's been about 1 week and the fondant has not hardend yet. What is the norm for it to harden?

Thanks

Fondant does not harden. Gumpaste or a mix of fondant w/gp or Tylose will harden.
Fondant should stiffen enough to handle the item after that long unless it is very humid where you are.

Can I add tylose to ready made fondant?

I have added Tylose to store bought Fondant and had success

Tylose+fondant=gumpaste.