In Kimi no Na Wa, Mitsuha is able to save everyone in the town even as the comet fragments were falling. So I'd like to ask, just how long would the comet fragment take to fall, in a timeframe that still allows everyone to reach the High School before the comet strikes?
Personally I think the comet's fragment has gone through a full orbit around the Earth, because it is unlikely that it has diverted so much from the original comet trajectory (which is tangential to Earth) to fall almost perpendicularly, since the break was above Japan and the fragment also fell in Japan
So it is likely that more than an hour has passed between the break and the impact.
By the way, I'm not an aerospace engineer, maybe my reasoning does not make sense ^^