How fast will the sun grow when it becomes a red giant?
Yes, the time is very long, but exactly how long depends on when you "start the clock" for the expansion to a red giant.  If you take the end of the "main sequence" (when the core hydrogen runs out) as the start of the expansion phase, it's more like a billion years to complete the process of becoming a maximally expanded red giant.  But the answer that gets 5 million years focuses only on the phase of most rapid expansion (which begins after the star is already quite a bit larger than the Sun).  Either way, our lives a the smallest blink of an eye to a star!