Don't see how it matters much either way. Pretty sure that once a species hits the point where it can remain unchanged for at least 500,000,000 years then they're pretty much biologically and technologically static (or stagnant, depending on one's point of view ). An extra zero on the end of that won't make much of a difference in the grand scheme of things. Contrary to what certain sci-fi properties would like to claim, it's very unlikely that a species with spontaneously evolve into non-corporeal beings if they exist for long enough or "achieve enlightenment".
There's a school of thought that says that once a species discovers tool use their evolution begins to slow down as evolution is largely a response to changes in environmental variables and technology by it's nature alters the environment to suit the species that uses it.
Apply that to a species that achieves total mastery of their environment (including genetic mutations) and you have a species for whom natural evolution has ground to a halt. So long as their genome doesn't break down, they could potentially (if they're *extremely lucky*) remain unchanged until the last proton decays. To such a species, a few billion years is nothing.
