In excess of 30 hours to create all the artwork and do the printing and weathering, but difficult to calculate really; probably more like 50 or 60 with numerous rewatches of the episode, research, sourcing materials and creating and attempting to source stuff that didn't make the final cut.
I actually drew a bunch of sketches of angels, the Doctor, Billy and the Tardis surrounded by angels, but they didn't really cut it, so I roped in a friend to do them, but he bailed too. There was going to be some stuff on various real weeping angel statues from around the world, but I couldn't get that to work satifactorily, so dumped it.
I also spent some time working on reproducing Sally's driving licence from the episode, but without a plastic card printer I dropped that idea. Pity, that would have been a neat little prop.
So, yeah, a lot of hours, basically!