Assume you have a collapsing star of around 10 solar masses. It cannot form a neutron star (too big) so it collapses down to thousands, then hundreds, then tens of Km in diameter. The Schwarzschild radius is maybe 50 Km. [I don't have an exact figure, but the formula is r=2*G*m/c^2. ]As matter is rushing inward towards this 50 Km target, time as viewed from a nearby inertial frame of reference slows right down. As an observer we see the light from the matter shifted to deeper and deeper red. Although we won't see it, right at the event horizon the light would be shifted to zero wavelength, zero intensity and the matter would be stationary. This corresponds to time standing still in our frame of reference. We know that time continues to pass in the frame of reference of the matter itself, but that isn't the point. For us, no matter can cross the event horizon within any finite period of time eg the life of the universe.Another way to look at it: just before a 50 Km event horizon exists there was a 49 Km event horizon, with lots of the mass still outside and unable to reach the event horizon within the life of the Universe. Before that it was 48 Km, and 47 Km, and so on. There is no way for the event horizon to get started.

My guess is that most of what we know of as candidate black holes are actually "candidate black holes in the process of formation". Maybe in the time available they have spawned an actual microscopic black hole with lots of mass just outside the event horizon; maybe they don't even get that far.

I can't find any detail commentary on this. Everyone acknowledges the time dilation, but they fail to comment on its implication related to the life of the Universe.