Regarding first timers and lower Antelope...
Upon your first time down there, particularly, if like in my case where it was my very first slot canyon, the tendency is to be overwhelmed and shoot like crazy. Lower is a place that I think demands a second if not third and subsequent visit so you can "see" without feeling rushed. Personally 2 hours is not enough to do the whole thing end to end. The canyon is slanted (down if you go in the traditional way) so be aware that if you go down and then come back the way you came in that the return leg is slightly uphill and you'll feel it
So I think compressing your time a bit in some bits and exploring a bit longer with shots in other bits is the way to do it, and I think having been down there once (or more) helps with that process to identify which sections you wish to really spend time on. I've only done it from the front (regular way in) down to the point right before where you would start to climb the several flights of stairs back and then turned around and worked my way backwards to the front. This is personal preference, but for me the canyons topology and shooting interest lie from just a bit beyond the traditional entrance through the super twisty/tight part to roughly the 2/3 or perhaps 70-75% through area and then the top opens up and the light and formations aren't quite as interesting. For me, going down the regular way and then backtracking back to the start forces me to "see" everything in a second way and in a second type of light and that helps me get some things I might have missed while trying to push through the canyon the first time. So my recommendation for those who are on their first time in the May or September time frames (the two months I've visited) are to get there EARLY (7:15 in the lot, so you're first in line when they open the gate at 8-ish (and it's a soft open, don't expect them to be open at 8 on the dot) and thus first in line at the booth and in the first group down), and try and hold off going crazy shooting for the first 100 feet. Going in the traditional way, you'll squeeze through the narrow rock entrance, go down the first and second ladders (watch your head on the first, particularly if you come back out this way), shoot a tiny bit then, then work your way down another ladder and then you'll be where you can start to see things. I think the tendency is to over-shoot a bit (naturally) until you get down the third set of ladder/stairs. Once you're down there, if you keep going a bit, you'll find the keyhole / eye/ window that occasionally gets a sunbeam between 10ish and 11ish in May - ask the guides for the hours (although I prefer the light in the canyon overall before then). From the eye/keyhole/window onwards you should be shooting a lot, exploring like crazy, different angles, etc. At some point the canyon gets really tight and narrow, and there are a couple of interesting shaped openings you can frame with awesome reflected light in the background, very red/orange and strong. I think one is before the gnarly twisted/dropping section (about a foot or two wide and angled) and one is after, but I haven't been since last May so my memory might be off. That section - from before the eye/window through to the section somewhat after the gnarly tight spot is IMO the best part to photograph - once you go much past this is when it gets a bit less magical. But that's just one guys opinion.
50 bucks or more to get the 2 hour photo pass, must have DSLR and tripod, is what I'm hearing these days.
-m