Does the centre charge a full day? They will claim for 12 hours (or whatever their full day is) so that will be submitted in their usuage, whether your child attended for all of those hours or not.
If you are putting in say $60 for the charge and then 10 hours, the amount you pay will differ if you put in $60 and 12 hours because the hourly allowance will be different. You get allowed (not sure exacltly how much) $3.60/hour, so if you put in 10 hours it will work out the allowance as $36, if you put in 12 hours if will work it out to be $43.20.
The ccb will go up the more hours you use, the ccb% is income based so it won't change when you change the hours of use.