Legal Question in Construction Law in Illinois

Do you have a written contract; if so it will control if there is a provision in it.

If you do NOT have a written contract, and you and the homeowner did not agree to any particular terms, what is reasonable is what should control. So if you expected payment within a given time, what's good for the goose is good for the gander. The Illinois Contractor Prompt Payment Act gives contractors the right to start charging interest if not paid within 25 days after work acceptance, as an "outside date" rule of thumb, but if you expected your customer to pay you sooner, you should expect to refund within that sooner time frame.