If you own a contract at OKW and a contract at HH, only OKW points can be used for an OKW reservation at 11 months, and only HH points can be used for a HH reservation at 11 months. And being different use years, they would have a different member number, so you can not actually "combine" them for a stay, even at 7 month, unless you transfer points from one contract to another. The other easier option would be, at 7 months, to reserve some nights of your stay using the OKW points under the OKW member number, and some nights using HH points using the HH member number, and then have MS link the reservations, but you could not combine points for any one night. For instance a night requiring 15 points could not pull 7 points from OKW contract and 8 points from HH contract without a point transfer.
You'd also have a different banking window for each contract.
While this works fine for many members, I personally like keeping my vacation planning more simple, so I would want the same use year.