I'm aware of the timescale involved. But there is still a sequence of events over that timescale and the question of what the collapse looks like on a microsecond scale.
The timescale can be best described as "By all means instantly". See above how composite structures fail. Its not like its first gets a bit wet and then more and more leaks open (and at this pressure, even tiny leaks can cut through humans and fill a small volume with water in minutes).
First you hear nothing special, the usual sound of the pressure vessel getting compressed just changes subtle and becomes sharper. Still no leak. But the first small fibers are torn. Now its the moment that you should surface ASAP and pray that the many layers and 5 cm thick hull are enough.
While the failure goes on, more and more fibers will break from the outside to the inside. All the crew inside notices about it, is the sound. The frequency at which the fibers fail increases exponentially, the integrity of the hull drops fast and then, all breaks in a few milliseconds. Especially if its also cold outside, the material will not be very elastic and simply scatter into small pieces when the energy is released.
The air bubble protected by the hull will simply collapses to a fraction of its volume, the persons inside not even have time to think about explosive compression. At these speeds and pressure differences, the crew is likely turned into jelly within a blink of the eye.
If you would have a 1 km (vented) tube, and fill it with water at that pressure of about 20 MPa, its completely filled within 1/6th of a second.