The band is pretty accurate. We know at what point it will intersect Earth’s orbit to a high degree. We don’t know what time it will do so. If it passes by soo

The band is pretty accurate. We know at what point it will intersect Earth’s orbit to a high degree. We don’t know what time it will do so. If it passes by sooner or later than the critical window, it will miss. If it passes by while Earth is in the way, the location will be determined by Earth’s rotation and exact position in orbit. That last part is the uncertain bit.