Even if you apply online, you need to send all the certified hard copies to ACS after you submit your application online. You will receive an email with the reference number of your application. You have to take a print of that email and attach to your certified copies and send them to ACS. Once they receive the certified copies along with the payment, then only they will start processing the application. Note their time line starts once they receive all the required documents and payment.

Hope this helps