In IL they will allow you to get behind as long as the other parent isn't pushing it and Public aid isn't involved.
I no longer live there but dealt with it during my custody case. He was ordered to pay and did for 3mo, then quit. In order for me to take any action I'd have to go there, set a court date and come back for it. However I do get the pleasure of listening to him complain of how his other baby mama takes him to court monthly, every time he misses a payment she's there waiting on the courthouse steps. He has been arrested and lost his license over it. I don't blame her. I just don't have the time or patience to deal with it nor him!
I knew when he was ordered to pay that he wouldn't keep up with it. He isn't a very good parent. That being said I have never included child support as a source of income and do not recommend anyone does. Even if it is garnished you still face a chance at it ending. If you want them to stop postponing it, speak up. Let them know you feel like he is purposely putting off getting a job and paying an that takes a toll on the kids. Speak up, they won't bite. If you sit there without hesitation they will just keep dragging you back. Tell them your tired of taking time off work to make a court appearances for someone who won't take care of their kids. Why should you have to continue to lose $ and make sacrifices?
In the future do not depend on him to keep up with any end of the bargain. He's proved he's not reliable.