No matter how detailed calculations can be, it is impossible to know how accurate they might be, given that we can only use the information available to us now, to make the calculations. We don't know what new information will come along with the passage of time that might affect those calculations, so it isn't wise to try to use calculations to predict future or even past events. Hence why the big bang theory isn't particularly wise.
It is even less wise to use such calculations to minimise our perceptions of the likely relative timescale of Earth existing as our habitable base planet in our minds, either, it seems to me, we could do with more reasons to believe Earth is worth saving right now, rather than less.
The calculations you refer to can't know the possible effects of humanity itelf on the longevity of Earth, other than than make an assumption that we are of no consequence at all, making no difference.
Isn't that a little like estimating the lifetime of a property without taking into account the effects of the residents living within it?
It seems to me we are at a moment in time when this question is being asked of us as a species, by nature.
It is up to us how we answer it. There are two possible answers, but only one is right
Are we here to destroy Earth, or to protect it?
It obviously makes a huge difference.