This depends on the orbit of the debris and the probability of getting hit (you are unlikely to ever get to 0, and technically, it makes little difference if you got a man-made bolt hitting you at 1km/s, or a naturally-occuring space rock of similar mass).
Most spacefaring countries have adopted a rule of getting low-earth-orbit objects out of space within 25 years of their mission's end-of-life.
Some (though relatively few) objects are in high orbits. These will take millenia - the good news is that they are also relatively slow, which makes them easier to avoid.
And then we have people shooting their sportscar into space on an orbit that will last virtually indefinitely.
> the good news is that they are also relatively slow, which makes them easier to avoid.
This is not true. Higher orbits do circle the earth less frequently...but that is not because they are slower, but because they have further to go. In fact, the higher your orbit, the faster you are going.
Most spacefaring countries have adopted a rule of getting low-earth-orbit objects out of space within 25 years of their mission's end-of-life.
Some (though relatively few) objects are in high orbits. These will take millenia - the good news is that they are also relatively slow, which makes them easier to avoid.
And then we have people shooting their sportscar into space on an orbit that will last virtually indefinitely.