Canyoneering is a TEAM sport
While other sports focus around the talent of the individual, Canyoneering in comparison, focuses on the group. While you may be the 1st person down the rappel, you still have to wait until everyone else has rappelled so that you can retrieve your ropes and then can proceed onward.
Everyone's safety is tied to each other. This isn't a fend-for-yourself type of scenario. If someone in your party hurts themselves, now it is up to EVERYONE to help and rescue them and call for help.
It's ideal that everyone in your group knows the "essentials" of canyoneering. That way everyone can contribute to the effort of the descent by being efficient with their skills and especially at rappelling. All of these efforts will yield in reducing time off of your estimated time of completion. (Wouldn't it be great to finish a canyon ahead of schedule? Now you will have more day-light to hike out in, more time for your next canyon, or more time to relax at your campsite.)
At rappels, while one person is rappelling down, another rappeller who is already at the bottom can scout a little ahead and see if the next rappel is close. As an idea perhaps, if the next rappel is close (which sometimes they are), that person could setup the next rappel with a second rope and have the next members of your group continue to rappel. This could cut your rappelling time in half once you master this technique.
The biggest time wasters in canyoneering are the rappels. If there is any chance you can perhaps down-climb instead of rappel, or even have two rappellers going at once, you can drastically shave time (which is a good thing).
For a personal example, I have once down Imlay canyon which took close to 17 hours to complete our first time through with a group of 6! The second time through and now with the aforementioned techniques now in places, we shaved it down to 8 1/2 hours. That's nearly in half!
I have also done the Subway in 6 1/2 hours with an efficient group of six friends versus a time of 12 hours with a group of eight. The biggest time waster that day of was the beginners at the rappels and waiting for that same group of 12 to proceed through the narrowest part of the canyon.
The more efficient your group is, the quicker you can descend the canyon and can add to your overall enjoyment of the canyon. Keep that in mind!
Remember this adage for all your canyoneering and hiking trips - you are only as fast as the slowest person.