It depends on the mass of the black hole. Typical lifetimes are ten to the power 100 years.
Science at this time can find no end to black holes. They seem to last forever.
A supermassive black hole is a an extremely large black hole, in the order of possibly billions of solar masses. They are thought to have formed from stellar black holes that managed to absorb enough mass from other objects, even other black holes and that they, without outside forces, can go on forever because they're so large that they absorb enough background radiation to compensate for the mass lost from radiating Hawking radiation. It is also thought they may have originally formed from black holes from collapsed gas clouds. There is thought to be a supermassive black hole at the center of every galaxy.
Without an early presence of black holes, it is impossible for galaxies to have formed. No galaxies, no heavy elements near Main Sequence Stars. No such elements near stable stars, no rocky planets that have the time to develop life. No life, no observers. So, black holes are "fundamental" in the sense that a Universe without them would be a Universe without anyone to recognize that there were no black holes!
They will remain as black holes for a long, long time.
It is uncertain how supermassive black holes form. Some scientists suggest they form from the simple collapse of clouds of gas too massive to form stars. They might also originate as large stellar mass black holes that form the the deaths of massive stars and the merge into a single black hole. All supermassive black holes grow by consuming more matter.
You could use a = V/t by substituting V for the speed of light, and then use t = the time it takes light to go through the event horizon from when it first crosses the Gravitational field.
There are currently space-born science packages that are searching for this very event - detection of such has not been successful to date but NASA's FGST gamma ray telescope launched in 2008 is looking for what is believed to be the characteristic light flash from them.
Black holes. They can be so large that they can suck up universes at a time
Here are some things that are currently unknown. * How do supermassive black holes form? * Are there intermediate-mass black holes? It seems there are, but this isn't very certain yet. * Are there primordial (miniature-size) black holes? These may have formed during the Big Bang, but none have been found yet.
Black holes do distort time. The closer you get to the event horizon of a black hole, the slower time goes. From the perspective of someone outside, time at the event horizon stops.
At any time.
Black holes were stars that were so massive that they collapsed on itself. The gravity in black holes is infinite and more you get closer to it, more time gets slower. Black holes suck all matter that is too close. Even light can't escape Black holes.