A World Passport Collection exchange that DVC MS faciliates through Interval International is always a 7-night stay.
Each II-affiliated resort that you would trade into can set their own check-in days. For example, for Marriott's Newport Coast Villas, the check-in days are Friday, Saturday, and Sunday. You can look it up online.
I think through INTERVAL, you can only check in FRI, SAT or SUN. With DVC and other timeshares DIRECTLY, you can check in any day of the week you like.