Day 110, 12:00, for 18 hours: 321 zombies at ×23 health and ×26 attack.
Part of Endless tier 22, day 5 of 5.
When it ends:
All-Purpose Strengthener
Fine Sheet Metal
Tempered Glass
Scrap Metal×3
Broken Glass×3
Electronic Components
Cold Cuts
Mystery Novel (Endless rewards, tiers 20-29)