Agreed, momof4....
I would give them a notice in writing stating that hours of operation are.... and that you are no longer able to accomodate such late pick ups. You may lose them, so I suppose this is where you decide what is more important.
Personally, there is no way that I would work a 12 hour day like that. I am surprised that they don't have one parent drop off and one parent pick up. That is the common solution around here to this type of problem.