It's called testing. I've found on other airlines that as long as you are 3 days before, i.e anytime after midnight, then they upgrade. Don't know how sticky CP is. Generally they look at departure date and subtract 3 days regardless of time, so for the 25th anytime on 22nd should be OK. The best way is to try it (just after midnight)--what have you got to lose?

I have even phoned an eastern call center from the west after it has turned midnight in the east. Now who knows where those call centers are. I have been asked what time zone I am in.