So I call midnight on the 4th day prior to departure, or the 4th day including day of departure? I want to try to upgrade AC850 YYC-LHR on the 27th, so what I understand is that I should call 12:01 am on Monday Calgary time, right? So stay up Sunday night...

I hit the sheets early, so I don't want to stay up, if it's the wrong day. I have read the FAQ, but I'm still confused. I always just got gate or op-ups/yup before.

Thanks in advance...