Day 49, 12:00, for 12 hours: 35 zombies at ×11 health and ×9 attack.
Part of Endless tier 10, 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)