Anyone know is the purpose of waiting 5 hours to charge the battery back up? I thought leaving a li-ion battery drained is bad for it. Or is it critical that it isn't completely drained but just at the auto sleep mark?

Agreed - once this is back in place, the system is energized, you run the risk of creating little sparks or worse if metal objects such as cover brackets accidentally touch areas of the logic board.

What is the reason for waiting 5 hours after it goes to sleep due to low battery in the calibration stage? I thought li-ion batteries weren't supposed to stay drained, ever.

If you have non-security T6 and T7s, carefully drill away the middle of the screw with a very small bit, stopping frequently to vacuum out the filings to see if you’ve done enough. You don’t need to do much, and too much will strip the screw entirely. Then very carefully unscrew using a T6 (you may need a T7). I’ve done it twice and it works.

Galvanic, it pops in.

GalvanicMacPro, to my recollection, the plate needs to be more fully inserted before all screws will line up again.

When replacing the keyboard ribbon, place a rubber band between the ribbon and your spudger to get the traction for a good connection.