If you find your suggestion of 10 hrs open missleading, then do not even mention it. Just stablish your hours and thats it. Unless you are open 10 hrs. But everyone has different contract time agreements. Ex 7:30 to 4:30, 8 to 5, 9 to 6, etc. I have tried that but to keep up with my records was also extra work. But I have charged accordingly. I will bill my 9 hrs of service plus extra time if they were late(with a recorded date and pick up time). You can also stablish a 9 hrs rate 9 and a half, and 10 hrs rate. I think parents will be more helpful if you give them the choice to decide to pay for 9hr. Service or 10 hrs.