While every circumstance is different, child support and child care expense are 2 different things. The only way to change his support obligation is to go back to court.
Child CARE on the other hand is extremely simple and can change day-to-day. The way we handle it, it the provider collects half from each of us. we pay separately and possibly on different days--I don't know or care when or how he pays. I just lost my job 2 weeks ago and if he chooses to keep them in care while I am at home because he doesn't want the girls with me on HIS days, his lawyer told him it would be his sole expense since I am available to care for my own children and daycare would not be necessary.
Anyway, when my youngest starts kindergarten in the fall, any childcare expense would be split still, but support will remain the same until we go back for re-evaluation after the 24 month period is up, if we so choose.
My friend's ex lives out of state, and child care is before and after school and some Saturdays. She pays the entire expense and he reimburses her after much scrutiny and harrassment.
Hope this helps. --C.!