An event horizon starts at precisely the moment a singularity does. The event horizon isn't so much a thing as a place. Like the Earth's Equator. It is the result of the singularity's gravitational pull and it will remain as long as the singularity does.
Event Horizons BBS ended in 1994.
Event Horizons BBS was created in 1983.
No. Only black holes have event horizons.
end of this year or the start or next year
there are 4 horizons
No, white dwarfs do not have an event horizon. Event horizons are a characteristic feature of black holes, where the gravitational pull is so strong that not even light can escape. White dwarfs are dense stellar remnants, but they do not have the extreme gravity needed to form an event horizon.
A and O horizons
Burning Horizons was created in 1993.
Reaching Horizons was created in 1992.
UK Horizons was created in 1997.
UK Horizons ended in 2004.
Unknown Horizons happened in 2008.