Why isn't a timeless being evanescent?

I think God is timeless. For a long time I’ve been vaguely worried by the thought that on a B-theory of time, a timeless being is like a being that exists at only one instant of time. But the latter being is really evanescent, while a timeless being is the opposite of evanescent. What’s the difference?

We can say: well, a being that exists at only one instant will cease to be when a new instant comes, but a timeless being won’t cease to be. But now imagine a being that exists at only one instant, but that instant is the very last instant of time. It’s no longer true that that being will cease to be, because to cease to be there has to be a future time at which one does not exist, and at the last instant of time there is no future at all. Yet the being that exists at the last instant of time is still evanescent.

If one believes in a “flow of time”, one can say that a timeless being is like a being at an instant of “time” in a “time” sequence that doesn’t flow (so it’s not really time, but only “time”). But a “flow of time” is hard to make sense of.

Here are two alternative stories. First, we might suppose that instants of time can have a “duration weight”. Thus, while one might think that the duration of n instants of time is always (in the most natural units) precisely n, one might think that instants have a duration which measures how long they endure. It’s not that they are exactly intervals. It’s still going to be the case that no change is possible during an instant. But perhaps duration is possible. Then on a discrete theory of time, a sequence of instants has a duration equal to the sum of the durations of the instants. And on a continuous theory of time, the temporal length of a segment of intervals is equal to the integral of the durations.

We can then say that a timeless being is like one that exists on an instant of infinite duration, an instant that has nothing before it or after it. On a discrete theory, this is straightforwardly just an infinite duration. On a continuous theory, it would be like a Dirac delta.

Second, we might hypothesize that what yields the subjective experience of “moving on” from one instant to another is the poverty of our experiences contained in the instant. But mystics talks of being caught up to eternity in their experiences of the infinite: time appears to slow down for them. But the experiences of mystics do not, after all, comprehend the infinite. However, perhaps, an experience that did comprehend the infinite would slow one down to the point that an instant would literally last subjectively for eternity. And this subjective time could then be an accurate reflection of the internal time of the being. If so, then only a being that comprehends the infinite, like an infinite God contemplating himself, could be timeless.

(Note that there may be some difficulty in fitting the above to the common observation that time flies when you’re having fun. But it has been hypothesized that the latter is due to the fact that when you’re having fun, you fail to notice every tick of your internal clock. Thus the fact that time flies when you’re having fun isn’t merely due to the richness of the experience when you’re having fun. It may be that what we have is a kind of phenomenon where modest finite fun makes subjective time go by faster, but then once we transcend fun into a mystical experience, the opposite happens.)