Day 69, 12:00, for 12 hours: 53 zombies at ×15 health and ×13 attack.
Part of Endless tier 14, day 4 of 5.
When it ends: 
Scrap Metal
Broken Glass
Door Repair Kit
All-Purpose Strengthener
Fine Sheet Metal
Instant Rice
Entertaining Magazine (Endless rewards, tiers 10-14)