Complex sentence: The red-giant phase typically lasts only around a billion years in total for a solar mass star, almost all of it spent on the red-giant branch, with the horizontal branch and asymptotic-giant-branch phases tens of times faster.
Split into simpler sentences: The red-giant phase typically lasts only around a billion years in total for a solar mass star, almost all of which is spent on the red-giant branch. The horizontal branch and asymptotic-giant-branch phases proceed tens of times faster.