Yeah. That's leagues better than what I get in Taiwan. The alert often arrives when the building is shaking or even after. I've never had a meaningful headstart.

I usually get it a few seconds ahead of time at least, in Taipei. I figured it's more related to the proximity than anything else.

It would seem the forewarning depends a lot on the distance from the epicentre. This quake, for Tokyoites, was far enough from them that they could beat the earthquake's speed. I'm fairly certain the people on the East Coast near the quake got no notification ahead of the event.