I've gotten images in as short as one day using a pinhole and exposing directly to Ilford paper.

Might be worth mentioning that you don't need to use a pinhole. I used a homemade lens/cigar box combination and got this in just about three hours:

The aperture is about half an inch and focal length (depth of the box) is about four inches. So that's ~f/8. Again the exposure was direct to Ilford paper.