[bruce511]

17 hours sounds like a long time, but it's not like there's a big red button and a guy standing by to press it.

So the information chain, starting with the telescope that detects the flare, and then has to work it's way up the food chain, so that sufficient people agree, and take presumably synchronised action, well, good luck with that.

You'd also ideally need a multi-hour warning, planes gotta land etc.

Make no mistake, shutting it down will result in some deaths [1]. And those deaths will be on the news tomorrow (if indeed news still exists.) On the other hand not shutting down will cause more deaths and massive destruction.

[1] think hospitals where the backup power failed, or didn't last long enough. Traffic intersections. Elevators. Water pumps. Airplanes. Trains. Take your pick.