Day 207, 12:00, for 8 hours: 216 zombies at ×41 health and ×44 attack.
Part of Endless tier 40, day 12 of 20.
When it ends: 
All-Purpose Strengthener
Fine Sheet Metal
Tempered Glass
Scrap Metal
Cold Cuts
Mystery Novel (Endless rewards, tiers 30-40)
Day 207, 12:00, for 8 hours: 216 zombies at ×41 health and ×44 attack.
Part of Endless tier 40, day 12 of 20.
When it ends: All-Purpose StrengthenerFine Sheet MetalTempered GlassScrap MetalCold CutsMystery Novel (Endless rewards, tiers 30-40)