Between the fact that we purchased these 3 days apart and have to do staggered comparisons and, well, life.. the check ins we are doing are 3-7 days apart.
Day 10 update.

Happy Meal Day 10:

Happy Meal Day 10 notes:
Fries are hard as a rock. They smell fine and continue to look good. My young daughter wanted to eat them.
The hamburger smells okay, the bun smells stale. The patty shrunk and darkened. No signs of mold.

In-N-Out Burger & Fries Day 10:

In-N-Out Burger & Fries Day 10 notes:
Fries are hard and wrinkled. The container for the fries is wet with grease. The fries smell old and stale. The hamburger smells bad. The bun is hard as a rock. The patty has darkened and there are 2 small mold spots have appeared on the patty, and are mirrored on the inner part of the bun. Some of the other white spots in the photo are bits of bun stuck to the meat patty.

Day 3 update.

Happy Meal Day 3:

Happy Meal Day 3 notes:
Fries smell still smell good. To the touch they are getting firm. The color doesn’t appear to have changed, but the photos will tell over time. The hamburger smells okay and looks okay It’s getting firm, but there were no signs of mold.

In-N-Out Burger & Fries Day 3:

In-N-Out Burger & Fries Day 3 notes:
Fries smell okay. They are greasy and getting hard. Some are soft still. Hamburger smells bad, stale. Bun is getting hard. No signs of mold.