Speaking somewhat loosely, I think we may say that the

processes of evolution from an extended nebula to a condensed
nebula and from the latter to a spherical star, are
comparatively rapid, perhaps normally confined to a few tens of
millions of years; but that the further we proceed in the
development process, from the blue star to the yellow, and
possibly but not certainly on to the red star, the slower is
the progress made, for the radiating surface through which all
the energy from the interior must pass becomes smaller and
smaller in proportion to the mass, and the convection currents
which carry heat from the interior to the surface must slow
down in speed
Speaking somewhat loosely, I think we may say that the
processes of evolution from an extended nebula to a condensed
nebula and from the latter to a spherical star, are
comparatively rapid, perhaps normally confined to a few tens of
millions of years; but that the further we proceed in the
development process, from the blue star to the yellow, and
possibly but not certainly on to the red star, the slower is
the progress made, for the radiating surface through which all
the energy from the interior must pass becomes smaller and
smaller in proportion to the mass, and the convection currents
which carry heat from the interior to the surface must slow
down in speed.