I'm at 85 boxes now myself, should be able to push through to 100 with the remaining days left. Know it's going to be a borefest in opening the boxes though, so many trips to the shop to burn the Silver XP, than shove a lot of the initial Gold XP into the 2nd Archive first before using the rest to keep leveling Servants.
Still, I'm satisfied with my grinding; I initially came into GilFes thinking I'd be happy if I managed to get 50 boxes.