Day 70, 12:00, for 18 hours: 144 zombies at ×15 health and ×13 attack.
Part of Endless tier 14, 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 Rice
Entertaining Magazine (Endless rewards, tiers 10-14)