alt Hacker NewsIt sounds impressive but it's worth considering that this was a large quake that was felt by basically half of the country. You do not get this much warning if you are anywhere near where damage happens.
The 45 seconds is better thought of as the time it takes for the quake to propagate to Tokyo
TBF you don't need substantial structural damage for falling objects to pose a serious hazard. Plus the relationship of warning length to extent of damage depends entirely on the strength of the earthquake. For the worst ones where you need it the most the majority of the country could get a fair bit of warning.