September 15, 2017 @ 12:00 am - September 16, 2017 @ 12:00 am S Corporations: File Form 1120-S if you timely requested an extension – see Form 7004
September 15, 2017 @ 12:00 am - September 16, 2017 @ 12:00 am Partnerships: File Form 1065 if you timely requested an extension – see Form 7004
September 15, 2017 @ 12:00 am - September 16, 2017 @ 12:00 am C corporations: Deposit the third installment of your 2017 estimated tax.