Chase is nothing if not creative. Their latest bit of creativity that is aimed at increasing fees is to say that a payment is due at the end of business hours on the due date rather than the actual end of the day. Furthermore the end of the business day is in their time zone (EST) not the one that you are in. With electronic payments these days, the end of business hours is not the end of the ability to make a payment, so business hours shouldn’t be important.
I suspect that some bean counter at Chase figured out that quite a few payments were technically on time according to their old rules but could be considered late if they just changed their rules a little bit.