Day 90, 12:00, for 18 hours: 216 zombies at ×19 health and ×20 attack.
Part of Endless tier 18, day 5 of 5.
When it ends:
Scrap Metal×2
Broken Glass×2
Door Repair Kit
All-Purpose Strengthener
Fine Sheet Metal
Electronic Components
Instant Spicy Hotpot
Inspirational Story (Endless rewards, tiers 15-19)