both days are pretty calm regarding traffic at LUX
as there's only reduced pax service. Cargo is best around noon (1030-1400) on saturday with many incoming Cargolux 747s and also departing traffic. I don't have an exact list of what will be expected but normally there should be the mentionned Cargolux planes, a China Airlines 744, a China Eastern MD11, maybe some Air Atlanta and MK
Airlines 742s and the regular An-26. There are also regular nice surprises on saturdays like special service 747s or even An-124s.
Best spotting location at that time would be on the southern side of the threshold for RWY24 (if that runway is in use):
Have fun and good luck with the weather!