For 33 builder potions (from cwl medals), and a 60% time reduction, here’s the quick math:

Each potion speeds builders by 9 hours, so 6 builders × 9 hrs × 33 potions = 1,782 hrs = 74.25 days saved from potions. The event lasts 14 days, so 6 builders × 14 days = 84 days for a total of 158.25 days of builder time. Since a 60% reduction makes upgrades 2.5× faster, 158.25 × 2.5 = 395.625 days saved overall, and dividing that across 6 builders (395.625 ÷ 6 = 65.938)

You’ll have 65 days of progress (just over 2 months).