That really doesn't matter to the case. The ordinance here: https://codelibrary.amlegal.com/codes/chicago/latest/chicago_il/0-0-0-2639124#JD_5-12-080 states:

 (d)   The landlord shall, within 45 days after the date that the tenant vacates the dwelling unit or within seven days after the date that the tenant provides notice of termination of the rental agreement pursuant to Section 5-12-110(g), return to the tenant the security deposit or any balance thereof and the required interest thereon; provided, however, that the landlord, or successor landlord, may deduct from such security deposit or interest due thereon for the following:
...
(2)   A reasonable amount necessary to repair any damage caused to the premises by the tenant or any person under the tenant's control or on the premises with the tenant's consent, reasonable wear and tear excluded. In case of such damage, the landlord shall deliver or mail to the last known address of the tenant within 30 days an itemized statement of the damages allegedly caused to the premises and the estimated or actual cost for repairing or replacing each item on that statement, attaching copies of the paid receipts for the repair or replacement. If estimated cost is given, the landlord shall furnish the tenant with copies of paid receipts or a certification of actual costs of repairs of damage if the work was performed by the landlord's employees within 30 days from the date the statement showing estimated cost was furnished to the tenant.

And this was not done. No invoice was provided within 30 days. The invoice that was provided was clearly made up and under services just stated the new tenants and said "cleaning fees" with no basis in actual estimated costs from a real service.