I rarely change flights and dates at last minute and have no problem using up all my PPs. Right now I am sitting in an NH F cabin courtesy of PPs. I think the bigger factor that influences success with PPs for Polaris is not willingness to change day or time of travel, but the degree to which one wants an advance guarantee of sitting in J at time of booking. Unless one is prepared to waitlist and have some uncertainty of success then the PP Polaris upgrade yield would be low. Of course domestic is different animal and, as stated, PPs upgrade is largely an academic construct.