That's a bit short notice for me to get a day off work, but might be workable. The 20th would probably be easier to swing the day off.
They've got a pretty comprehensive website with all the info about taking photos there. When I went before on a weekday, the girl at the ticket counter was totally unfazed by my dragging in an 8x10 and tripod, but it was a very quiet day. She was amazed that I wanted to get the audio guide, since most photographers coming through seem to only want to take pictures and are disinterested in the history of the place (according to her). I found it very worthwhile to get the audio guide because it gave you an excellent overview of the history of the place, and made the things you were looking at make more sense. I also would have missed some details of the prison had I not had the audio guide.