Hi, it sounds like the ground settled on the outer edge of the pressure plates. That is fairly common. That probably would have happened no matter how firm the pool krete was. It is possible to drain the pool, just not into the deep area, repair and refill ASAP. I have done that. Or you could wait until your first liner change.

As for how long to let the stuff dry. I have very little knowledge there. I could not say for sure if that would have made a difference or not.

Hope it works out OK, Dennis