Thanks for the link! I have a coffee table book with most of those photos in it, but it's nice to know they're all in one place on the web. I also have a portable dark room that stands on tripod legs, but it doesn't have wheels...maybe I should add wheels to it...hmmm.
One of Roger Fenton's competitors would have been a man named Felice Beato. Beato has a Wikipedia page with some nice, high resolution scans of his pix:
http://en.wikipedia.org/wiki/Felice_BeatoAs for the exposure times, I would guess most them were between three and five seconds. Most of them look like they were done in direct sunlight, with the sun near its highest point in the sky. It also looks like he's using the widest aperture in his lens, because a wide aperture tends to exaggerate the effect of a spherical field of focus, which you have with a Petzval lens. The fact that he's shooting negatives (as opposed to direct positives, i.e. tintypes & ambrotypes) would normally require much longer exposures, but it's probably so bright and sunny out there that he's able to get away with fewer than five seconds. Of course there's no way to be sure without knowing what kind of lens he's using, but even then it would still be difficult to tell because each of those hand-made lenses were slightly different from each other.
The longest exposure I ever used with a human subject was two minutes. It was at a Civil War re-enactment with an overcast sky, and it was very late in the day. The sun must have been very close to the horizon, but I couldn't tell because of the overcast. I told the subject to lean against a tree and to breathe as shallowly as possible...and the resulting image wasn't half bad.