The billion year time span seems high compared to other sources. One 2008 textbook shows several hundred million years from the time a solar mass star leaves the MS until it goes through its helium burning stage, with the longest phase being the time when hydrogen is burning in the shell around the helium core (ie subgiant branch).
Originally Posted by m1omg
Arcturus is ascending up the RGB toward the helium burning phase. It is about 1.5x in solar mass, so it will have a hotter surface temp., no doubt, than the Sun will be during this phase.
The helium burning stage lasts for only a few tens of millions of years for a solar mass star.
We know time flies, we just can't see its wings.