Suppose there's a star out there that's a lot more massive than the Sun.
Suppose further that orbiting this star is a planet not unlike Earth. Water, oxygen, civilization, and all.
Now the star decides to go supernova. How quick, or slow, is the process?
How long will it take it to heat up to make life on that planet impossible? A month? A year? A hundred years? A thousand years?
And how long will it take for the supernova to engulf the planet? A day? A month? A year? A million years?