The member ownership percentages are directly related to how much time each person gets per month via the scheduler. We basically create two buckets of time - all the standard slots per month and all the premium slots per month. For each of those buckets, the member will get the amount of time equal to his ownership percentage.
At this point the system has had thousands of users so the allocation of fair percentages works well.
The scheduler also provides for swap requests (I want to trade a slot I have for a slot you have) wait lists (if you cancel your slot, i get signed up automatically), slot confirmation (you must confirm you slot in the time set or someone else can reserve it) and a host of other features.
I see you have an account in the system - so you can get in there and experiment with the scheduler settings, etc. Also, check out the expense tracker - we have just spent some time upgrading that section of the site and, while simple, it does do a good job keeping track of expenses in a sharing relationship.
Let me know if you have any other questions.