Day 82, 12:00, for 8 hours: 117 zombies at ×18 health and ×18 attack.
Part of Endless tier 17, day 2 of 5.
When it ends:
Scrap Metal
Broken Glass
All-Purpose Strengthener
Fine Sheet Metal
Instant Spicy Hotpot
Inspirational Story (Endless rewards, tiers 15-19)