"due day" is correct and usable in written English.
You can use it to refer to the day something is due or the deadline for completion of something. For example, "The due day for my project is tomorrow."
A few days before D-Day — er, due day — we scanned movie credits and newspapers, hoping another dark horse that had somehow escaped the baby books would emerge and win our hearts and minds.
Let him lie dead, Well before his due day, halfway up a beach and unburied".
When a ransom was not paid on the due day, he had 30,000 Muslim captives slaughtered in full sight of Saladin's army.
_____ As those of you who do the crosswords online will already know, some of them have not been appearing on your screens on the due day, including the Quick, the Quiptic and the Observer's Speedy.
To have two out of three declared candidates effectively knocked out even before the due day for formally declaring their candidacies, 26 October, makes its own statement: the organisation is nowhere near ready for an election of a president.
After generating multiple process plans, each process plan is allocated the possible manufacturing scheduling time and the candidate process plans are retrieved based on the required due day.
