I don't think Laura actually answered the question. I agree, like anything, practice makes us better at whatever we do, but how many hubs in one day?
You have not provided enough information to answer that fully.
You have not stated how long the hubs are meant to be (how many words), whether any graphics are prepared or whether they still have to be sourced or what the subject matter is, as this can greatly affect the length, need for graphics etc.
I was writing a couple a day, but looking over these hubs now, I realised that actually, I was't doing them justice. I found I spent a lot of time locating the graphical material and then rushing writing the hub itself, not filling it with meaningful, helpful and interesting content for the general public.
The hubs will not be picked up by search engines immediately anyway, so there's no real need to rush. Quality is far more important.