[ferelrossi]

How soon would we know about a gamma ray burst threat? If it's close enough to do damage, is it close enough for us to leave with warning?

I'm not sure but think there'd be very little warning.
But it's something that is a very remote chance, not really worth worrying about. It would be if we were closer in to the middle of the galaxy though, where stars are more tightly bunched-up.