I did AC's self-contained Northern Tier trip back in '99. Most of the sutff works itself out without many/any hard and fast rules.
They way we worked, it, you were paired with another participant. When it was your turn to cook/clean, up, you and your partner shopped for snack and dinner stuff that evening and breakfast and lunch stuff for the next morning. Others would almost always help transport groceries, especially when there was no opportunity to set up camp before shopping. Nothing was on a fixed schedule (e.g., dinner at a set time each night). It could depend on how long a day it was. People might not get to camp until later in the day. Since we usually bought snacks (e.g. chips and salsa) to tide us over until dinner, there was usually sometthing to get you through to dinner.
After dinner, the two cookis were also responsible for washing the shared cooking equipment (e.g., pots, pans, cutting board, etc.) and disposing of any trash. Each participant was responsible for washing his/her own personal plate, bowl, etc. to lessen the chance of mass contamination. The next morning, the same two were responsible for having the breakfast stuff "ready." Rarely did we cook breakfast. It was more like cold cereal. So for practical purposes, there wasn't really much to do for the two cooks. Also, participants prepared their own lunches to take with them. Usually PB&J, cookies and fruit. The early birds among us could get up when they wanted to, get their own breakfast, pacl lunch and leave whenever. The two cooks were again responsible for washing any group gear used to prepare breakfast and lunches. If it was your turn to cook, you couldn't really sleep in as late as you wanted since the person who, for example, carried the cutting board and group knives might want to hit the road and could not until that gear had been cleaned.
In response to a few of your specific questions, we only at dinner in the dark once or twice. Being on the Northern Tier helped. It usually didn't get dark until late. You were never required to be present at any of the meals, but the courtesy you mention was expected, in part so the cooks didn't over-buy and the group wasn't waiting around for you to show up. One hard rule that we did come up with was that when you reached camp or the town where we would be camping, you were required to off-load the group cooking gear you were carrying before heading off to explore. This made it easier for the cooks to do their jobs.
Remember that if you go on a long trip with 14 people, you are only responsible for cooking once a week, so the chances of that getting in the way of things are slim. Also, the group will realize that people ride at different paces. It's highly unlikely that you will miss dinner because people didn't feel like waiting for you to get into camp. Also, if it is your turn and there is something that you would really like to do that day, you can ask for a switch, either with the next pair or an individual.
As noted, everything usually works itself out with little problem. I took a lot of photos (about 100 rolls of film) during the trip and never felt rushed by cooking duties. And if an overnight sidetrip was desired, a person could usually get a sub to cook. The biggest propblem we had, on the meal front, anyway, was with one participant. He apprently felt that doing dishes was beneath him. On several occasions, he took a little bag of trash to the dumpster, considered his work done and jumped on his bike, leaving his partner to finish the morning's tasks. When we had to shop before reaching camp and then ride with groceries, he would rush to the shopping carts and grab the lightest items, such as the bread or nacho chips. Most of the time, we simply turned this into a source of amusement rather than get pissed off about it. That's probably the most important thing about a group tour: You need to try to not sweat the small stuff. I know, however, that that is sometimes easier said than done.