as pointed out by both @CWanamaker & @Chasuk pointed, it depends on the type of hub you are writing.
I takes about 10 to 12 hours, if I need to put a hub after some research and doing some images on the way. As my hub http://hubpages.com/technology/deep-search-people-... needed some extra hours as I dig deep into the net for the information and get the right screen captures.
Sometimes, it is breeze... just under 2 hours. My hub on Goa trip titled "goa travel for fun on beaches" was done in less than 2 hours, as i wrote it immediately after my trip there. I have added all the photos in this hub taken during my trip.
Here is one of the photo for you to enjoy...