Given a "Date Revision Due" for revised submission of a journal paper, am I required to submit before the beginning or the end of that date? I am submitting a revised manuscript to an Elsevier journal. However, English is my second language and I am confused about the meaning of "Date Revision Due"! 

The journal editorial system indicates "Sep 19, 2015" as Date Revision Due. Please tell me should I submit the revised manuscript before "Sep 18,2015 11:59 PM" or "Sep 19,2015 11:59 PM"?! 

I guess the local timezone of the journal should also be considered. In addition, Can I submit the revised manuscript by automatic editorial system even if I miss this deadline?
Unlike conferences, a journal's "date due" is rarely quite so precise a moment; this is because papers are all being dealt with asynchronously, on an as-arrived basis, rather than as a massive batch of hundreds all arriving near-simultaneously as for a big engineering conference.

Most journals will be comfortable with you submitting a little late if necessary (though there are some that will automatically discard your paper if you don't hit their deadline).  Thus, rather than fretting about time-zones, I would recommend that if you are worried about a last-minute submission, you instead email the handling editor and ask for a short extension.