How much advanced notice would we likely have in advance of an Earth bound impactor with a place of origin outside Earth's orbit (e.g. a meteor, asteroid, comet, space debris that doesn't rotate around the Earth) of 100 to 1500 meters in diameter with astronomy technology that currently exists or will exist in the near future (i.e. next decade or so telescopes and computing technology with non-vaporware instrumentation that is already in advanced planning stages)?
What is the range of time frames in which we would likely have notice (presumably there would be some variability)?
What factors would influence how much advanced notice we had of such an impactor with current technology (e.g. direction of approach, current speed, composition of object, etc.)?
Presumably, we would have a more accurate estimate of where it would hit as it got closer at some time after we initially noticed it was heading in the general direction of Earth.
How much notice would we have before we could pin its impact point down to a roughly 150 km radius impact area on Earth?
Assume that nothing but gravity and its current position and velocity influence its route (e.g. not the case of a working space ship), and that there is no "tracker" on the object, or compact radiation source, that makes it easier to pinpoint its location and trajectory.