Letting new plaster sit for 6 hours before water is added lets it harden before being submerged in water, because it is very easy to dissolve the surface of fresh unhardened or uncured cement/plaster. If you fill the pool with a garden hose it can take 24 to 48 hours before the lower areas and steps get under water.
Once the plaster hardens after a few hours it can begin shrinking and can develop spider cracks. How long depends on the temperature and sun on exposed plaster.
It's the reflection (look at the flamingo float) - makes it look like the skimmer is completely open, because it's reflecting the open top half on the the water. Ours does that sometimes too, usually sending me outside to double check.