Re: How long does an average star remain a red giant before collapsing?

The answer depends upon the mass of the star. The more massive the star, the less time it spends in the giant phase. Unfortunately, the amount of time a star spends in the giant phase depends quite sensitively on the amount of mass loss that it undergoes, which is a process that is only poorly understood.

For reference, though, the Sun is predicted to spend just under 1.5 billion years moving from the main sequence to the white dwarf phase, with the vast majority of that time spent in the giant phase (Sackmann, Boothroyd, and Kraemer, "Our Sun. III. Present and Future").