I remember watching a program on tv, unfortunately not which specific program, where they tested opening the door of a car that was sinking by both waiting until the pressure equilized and trying to open it as soon as possible after entering the water (A pool in this case).

And I want to remember they had a very difficult time in opening the door of the car while it was still sinking, even though it was filled with water, until it touched down on the bottom. As the internal/external pressure was constantly changing as the car sunk until it touched down on the bottom.

Therfore it was concluded that attempting to open the door as soon as posible, before the car had a chance to truly sink and take on water, was the way to go. Of course, as soon as the door was open the car sunk quite quickly.