There are 2 distinct things that can happen on II with DC points-
1) MVC takes the number of points you choose and deposits the week size/ TDI you pick from the chart on mvc- (use points, interval international) into II. This exchanges as a week- no points involved at all- just like any other week except you can’t exchange into a Marriott. It’s good for 2 years so it’s a way to extend points. You pay an exchange fee except for Vistana and Westin, you can pay an upsize fee for a larger unit, you can buy eplus. I believe this would be subject to II’s regular cancellation rules.
2) You can do a points exchange with DC points on II- but you don’t deposit the points into II. I believe this is what bazzap means by “request first”- the points are still yours (as an undeposited week would be with request first) unless you confirm an exchange. In addition to placing an II request using the DC points you can do a manual search to see what is currently available on II using your points account. I have been told by MVC they they are not connected to II and MVC would need to be involved to confirm a manual exchange using points. Still can’t exchange into a Marriott, expiration date of points is unchanged. I don’t know what would happen if you cancelled an exchange made with DC points on II.