Estimated tax payments - which date do you use -- submission? or payment?

[kamull01]

When specifying the date of an estimated tax payment, do you give the submission date?  or the payment date?  I have a confirmation from the IRS for one payment where the two dates are different.  The submission is on a Friday at 8:00 PM and the payment date is the following Monday. 

[rjs]

Use the payment date.