I think it's important to organize a planning committee that has the time committment and dedication to this project. As we all know, people can get busy and have many tasks to focus on. In my experience in Greater Washington, we've split up the responsibilities and had a main event coordinator (yours truly) and other times, it's been myself and 2 others planning the entire event. Both can work, however, the more people who are involved and dedicated to the project - the better.
We usually look at the week after BGC Week to start forming the planning committee. Sometimes this has been too early and sometimes it's been too late. Actually this year, we started in December! We are partnering with a few other groups to present DFK '08 so we had to fit into their planning periods. We already have the location and most of the logistics worked out. So the earlier the better has worked out - however, once we get more direction from BGCA - we may have to tweak some things.
Overall, I would say organize a committee of dedicated and available people including staff members, parents, Board members, community members, etc. and get to work as soon as it makes sense for your organization. Have a coordinator who can keep everyone in line and focused and remain on task. (Those folders Meredith puts together are great! - the schedules can be incorporated into your organization's master calendar). Know and stick to your deadlines and maintain realistic expectations. :-)