As in not purchased in a Hermes boutique (e.g. Neimans, Decades, etc) or not a Hermes bag altogether?
If the bag is an authentic Hermes bag, then yes, they will accept it.
One member posted that her friend had purchased a Kelly years ago and had it dyed. Hermes refused to touch it. I guess because the dye can no longer be matched. Anyway, they will accept a bag not purchased at their store, as long as it hasn't been altered.
I can't speak for Paris but here in the states my SPA treatments have taken from 4 to 8 weeks and the cost varied from $80 to $100USD.
^^^ Yep! Which means you'd better carefully choose a period when you are almost sure you won't need to use your bag. And be ready to miss it a lot anyway! Here in Europe it's from 4 weeks to a bit more than two months.
The positive thing is that when the bag comes back the results are usually astonishing