Flying YYC to FRA on the 10th of April. Still lots of R class seats showing on Seat counter. Just wondering when I can actually call the airline to confirm an upgrade in the four day window for elites?

Is it the night of the 5th / early morning of the 6th or night of the 6th / early morning of the 7th?

I will actually be on a flight from YYZ to YEG on the night of the 5th (departs YYZ at 2240, arrives YEG 0026) so if it is the night of the 5th, do you think they would let me do it before my flight?

Thanks for any advice.