How fine is the black hole "point of no return"?

The event horizon is the "point of no return" around the black hole. It is not a physical surface, but a sphere surrounding the black hole that marks where the escape velocity is equal to the speed of light.

..."The point of all this is that it is basically what happens with a black hole. We've established that in the rest frame of an accelerating observer a horizon exists, and if you are hovering a fixed distance from a black hole then you are an accelerating observer so as a result a horizon exists. It might seem a bit odd to say you are accelerating when your distance from the black hole remains constant, but the key point is that general relativity does not distinguish between inertial and gravitational acceleration. Both are treated in the same way. I go into this in more detail in How can you accelerate without moving?"....

https://physics.stackexchange.com/questions/555212/why-is-there-a-definite-boundary-of-a-black-hole-that-marks-point-of-no-return

So basically as long as your engines are holding position and have enough reserve energy to escape the gravitational pull of the black hole you're good, once you get past that, you won't be home for dinner....So if you had an energy source that could accelerate past the speed of light, there would be no point of no return....so the point of no return is based on your spaceship design....

..."The fastest a man made rocket can go today is very roughly some 60,000 km/h*. At that speed you could orbit a black hole (B.H.) with a mass of 4,000,000 Solar masses (e.g. Sagittarius A at the center of our galaxy**) at a distance of 1.9 * 10^15 km. In more manageable figures you would have to orbit that B.H. at a distance of ~ 203 light years** at a velocity of 60,000 km/h, in order not to get “sucked in”."...

https://www.quora.com/How-close-can-you-be-from-a-black-hole-without-getting-sucked-in

sphere surrounding the black hole that marks where the escape velocity is equal to the speed of light.

Since we have recently observed some matter apparently escaping a black hole, does this imply that "stuff" inside the black hole can exceed the speed of light that we know about? Maybe it means that the speed of light, c, is actually a variable in a huge gravitational field?

Yes interesting, I look at it like when too much matter is captured by the black hole, the forces become so extreme that a huge vortex is formed at the poles, like a tornado in the event horizon, and the tip of the vortex then reaches the portion of the interior of the BH, where the matter is in a gamma state, and it releases the overburden in radiation bursts....interesting that a black hole has limits as well, it would seem an explosion is close at hand in these circumstances, and the interior of the BH is rapidly rotating, like water going down a drain...I believe magnetars, neutron stars and quasars all rotate very rapidly....

..."The fastest-spinning neutron star known is PSR J1748-2446ad, rotating at a rate of 716 times a second or 43,000 revolutions per minute, giving a linear speed at the surface on the order of 0.24 c (i.e., nearly a quarter the speed of light)."...

https://en.wikipedia.org/wiki/Neutron_star#:~:text=The%20fastest%2Dspinning%20neutron%20star,quarter%20the%20speed%20of%20light).

How small is the point where negative numbers become positive?

The event horizon is a three-dimensional transitional boundary. The simplest form of this equation assumes no rotation and is known as the Schwarzschild radius. This boundary layer is so thin that when a quantum vacuum fluctuation pair is formed adjacent to this boundary layer, the thinness of this boundary makes Hawking radiation.

So what is the diameter of one quantum particle,(just one of the pair)?

To my understanding,the pairs do not have to be adjacent to each other.

..."about a tenth of a billionth of a meter wide "...

The diameter of all of the Standard Model particles is much smaller than one RCH in diameter. I hope this is what you mean by a quantum particle.

If rotational velocity increases as matter is added to a black hole,then maybe the hole is a torrid shape,with new material adding to it's girth in all directions,and with increased velocity,all mass will be flung to the outer edges.At some point,the rotational velocity will equal the speed of C.What happens then?

That's just it, as it approaches C it regurgitates matter in the form of gamma ray burst from the poles....

If rotational velocity increases as matter is added to a black hole

But does it? Is angular momentum conserved? If the added mass brings angular momentum with it, it might be either + or - to the momentum that exists. But black holes are beyond my understanding, so all I can do is wonder!!

The speed of rotation of a black hole is determined by its mass...

...."One black hole, at the heart of galaxy NGC 1365 is turning at 84% the speed of light. It has reached the cosmic speed limit, and can't spin any faster without revealing its singularity."...

https://phys.org/news/2014-02-fast-black-holes.html#:~:text=When%20a%20star%20becomes%20a,rotation%20speeds%20up%E2%80%A6%20a%20lot.

https://en.wikipedia.org/wiki/Penrose_process

How does one adjust the time....and the space(length)....of a constant velocity? Put the velocity in a rotation and adjust the diameter. Natural calls this dynamic mass and matter. Charge fields scissor at c.

How does one mark the rotation so as to SET one rotation? Put a small loop in the arc of the rotation. NOW 1/2 the rotation leans to the right and 1/2 the rotation leans to the left. One rotation. A wobble marks RPM. That is a wobble, sets the rotational rate. Or frequency. The right EM field thru the center of the charge...can contract and induce another loop in arc of that rotation. NOW the charge has two wobbles per rotation. And the charge is smaller and rotates faster.......more energy. ONLY at least one full turn can be added or subtracted.......This is part of the digital quantum effect. One integer turns.

An electron has a small number of turns or wobbles. A proton has hundreds of turns and is small, hard and spins much faster than the electron.

The question that comes to mind is what is the point of knowing the boundaries if nothing can ever come back from the black hole?