Knowing the time doesn't tell you which side of the planet it will impact. The asteroid and the Earth are both moving. From the asteroid's perspective, it can g

Knowing the time doesn't tell you which side of the planet it will impact. The asteroid and the Earth are both moving. From the asteroid's perspective, it can get ahead of the earth and the Earth rear ends it, which from Earth's perspective is the asteroid hitting from the opposite direction that it's coming from.