As long as the floor: in other words, wall to wall.
24 feet long.
12-24 hours
Hmmm, I wonder just how long a plywood wall would last in ground or above ground for that matter? You might want to consult a pool builder.
15' x 24' oval pool with 54" wall has 8,823 gallons of water.
24 hrs
Long enough to turn over the full amount of water in the pool every 24 hours.
Hydralic cement?
I would think any material can be used as long as the pool wall is protected from scratching. A bigger issue is that you may be violating the building code by reducing the effective height of the pool wall. Most if not all municipalities require a 48" minimum height from the ground to the top of the pool wall to keep children from being able to climb in.
24 foot round pool would be 24 feet across from the middle of the pool basically measure the diameter of the pool.
With a standard garden hose, about 24 hours
Multiply the diameter by pi. 24 x 3.14 = 75.39 feet