30 seconds? you must be joking. I live in Japan and get such alerts on a regular basis. usually you get the alert about 3 to 5 seconds before the shake hits you depending on how far you are from the epicenter. If you get something 10 seconds before it hits then you dont even have to worry because it means you are very far.

Those 10 seconds were staged. She knew that they were coming, she was in a small "room", and she probably took a look at her surrounding before those 10 seconds kicked and planned what to do and in which order in her head.

In real life, the warning such as this would catch people by surprise. That's not to say they wouldn't be useful, but I highly doubt they would be that useful as they were on that video.

Even if I'm in my own home, I imagine it would take me at least a fifth of that time to look around and come up with a plan of what is achievable in such a short time span.

Why do you suppose she props the door open with the chair? Because building shifts could jame it closed via the door frame?

Yes, there have been cases of people getting trapped in rooms/buildings due to doors getting bent or warped, so it’s common advice in Japan to prop open a door to secure yourself an exit.

That's just Triangle of Life nonsense.

https://en.wikipedia.org/wiki/Triangle_of_Life

https://www.snopes.com/fact-check/triangle-of-life/

It isn’t about buildings collapsing, it’s about doors getting stuck, so I’m not sure what relevance the Triangle of Life has here.