It depends how bad the fungal infection is. It can take several months for the comb to heal because favus is layered on the comb/skin. I had one hen get favus in my previous flock and I caught it early but it still took 5 weeks to heal back to normal. That's all I know about it.
I dont recommend using ivermectin unless you've actually seen external parasites on your birds. Then if they have them, you'd have to treat their coop, nest box, roosts. Permethrin would be best, liquid or dust.
Keep in mind that Favus is a fungus.
A small tube of miconazole cream can be found in Monistat feminine products. You'll need to buy several packages due to the small size of the tube. Buy the cheapest you can find. You also might be able to order just a tube of miconazole online, be sure to check the size/amount if you order it...
That's not fowl pox. It's a bad case of Favus. Treatment is miconazole. It is contagious, make sure you wear disposable gloves when applying the miconazole.
http://www.thepoultrysite.com/diseaseinfo/59/favus/