If you decide to redeem your funds before 3 PM, then the NAV calculated later for that day would be applicable. If you redem your units after 3 PM on a day, then the next day's NAV would be applicable.
This happens if you buy or sell through on-line websites. Same thing happen if you buy through broker and your broker submits your application as per the above time line.

Hope I have made it clear. If still you have any question, Please post your question here in the forum.