All companies who accept credit account payments online set a "due date" that the monthly payment is supposed to be made on or before. Many of them accept payments that will post the stated due date only if the payment is made before a certain time of day. By doing this, they are able to impose late fees on their customers if the payment is posted after the cutoff time even if it is on the stated due date.
Payments should be accepted and posted on the stated due date up until midnight local time. This practice is simply another way for these financial institutions to fleece consumers who are already paying outrageous finance charges on consumer credit accounts.
I was recently charged a $25 late fee for completing the transaction less than 2 minutes after the "cut off" time.