If you call MS within 3 days of getting off the ship, you get a 10% discount on points.
I booked on-board for cash early in the cruise and then joined DVC. When I returned home, I call MS to get the discount but the points were not available at that time. When they did become available, they transferred my cash ressie to DVC. This was also a hassle because I had to put down a $1000 deposit for my cash ressie and had to have MS and
DCL on the phone together to get my $1000 credited back to my credit card. For some reason when the ressie transfered to DVC, the deposit did not credit to my account.
DVC members also flame other DVC members for booking the cruise with points saying it is a better use of points to rent them out and then pay cash. Our cash price was $4400 (with the 10% on-board booking discount) and our DVC points were around 450 (I can't remember exactly). At $10/pt for renting, it was basically a wash. I also originally booked on board within a week of the prices becoming available so there was not a price increase for cash. If I waited until now to book the cruise, it would probably be cheaper to use points because the points don't change but the price goes up as the cruise fills up.
If the points are not out for your desired sailing when you return from your cruise, I don't know what the policy is...call MS.