ديو إن تُستعمَل لمدى زمني غير محدد بيوم معلوم ، ولكن لليوم المعلوم يُقال: ديو أون
SO the correct way to say this is " it is due on Monday.
https://answers.yahoo.com/question/index?qid=20090208184148A...
a. Expected or scheduled, especially appointed to arrive: Their plane is due in (within) 15 minutes.
http://www.yourdictionary.com/due
it's due on the 30th
http://www.thefreedictionary.com/due