If the only issue is the date of the modification, this is simply a math question: are you going to spend more than $1100 in attorney fees by going to court. If it is set for a half-day hearing, the answer is probable yes. If your attorney does not feel you will win, he probably has a reason. It sounds like you have a lot more to lose than $1100.
Child support Child support and imputed income Child support arrears Child support modification Child support and changes in circumstances Child support enforcement Enforcing child support by contempt Penalties for not paying child support Lawsuits and disputes Family law Fees Contempt of court