I have had six hens with bumblefeet and three of them repeatedly.
It went from two weeks of healing to six months including a vet surgery. There is no average. A month is not uncommonly long at all.
I don't have a scientific knowledge to back this up but I have personally come to believe that it's not only about how you treat and how early you caught the bumblefoot, it also depends on the hen.
I don't isolate my hens and I let them free range with bumblefoot. I have very rocky land and I'm on an old farm where people have dropped pieces of mesh and nails for ages, so the hens get bumble feet a lot and don't heal the quick way.
I have tried all the various types of dressings suggested above and all the ointments and products available where I live (in France OTC antibiotics don't exist). I find hydrocolloid the most convenient but that doesn't mean they are a miracle. Just that they keep the wound cleaner and are easier to apply.
I leave them on for up to four days, but when I feel the bumblefoot is bad I change them daily or every two days, because the bathing in epsom salts really helps with healing.
I don't think there is one ideal remedy. For example sugardine did nothing for me whereas it was a game changer for other BYC members.
My vet's prescription was betadine and a sulfadiazine onguent, but I haven't found that the most efficient either after several tries. I also did not like using betadine long term so now I use it the first two weeks and switch to diluted tea tree oil.
I use a drawing salve when the bumblefoot is on top and there is no scab.
I still sometimes use corn dressings for my heavier hens or when the climate is really dry and I don't feel it's necessary to keep the scab as clean.
Unfortunately I think
@PopoMyers is right and you just need to be consistent if it takes a long time.
I can't say what it's worth as I did not try this : there was a post recently that said to gently brush in the neosporin with a toothbrush, so as to get more of it through the scab, and that it really helped heal quicker.