Let's say your dates of travel were Dec 15- Dec 20th . you call/ book online for 12/10 - 12/15 then on the next day at the 12/11 window you book for 12/11 -12/16 cancelling the 12/8 reservation.... and so on. (if you have a boat load of points you could potentially book on 7 days before, doing night at a time. (noting borrowed points stay borrowed, so don't mess up )