What does that say about the minutes it takes me to write this read these posts and write this response?
Why should a league have anything to say about a cubit? Really, both measurements are defined in terms of human utility - they say something about humans rather than about each other.
But here's the thing: a cosmological time-scale has no obvious human utility at the moment. Our appreciation of it is at best aesthetic, and pretty poor even at that.
Minutes however, have heaps of human utility. It's perhaps our most bargained (and stolen) measure these days.
The question of eternity? I agree actually (but that doesn't mean I won't ask the question, anyway; it matters to others).
We're writers; we're allowed to go on about meaningless stuff. It just behooves us to remember that beauty isn't always truth.
Time is interesting to me for a lot of the reasons you bring up. I wonder how irreversible it is in so far as we have managed it.
I smell a 'there is only the subjective' argument here.

I'd strongly disagree with it. Time forces us to agree with one another more than our self-interest would prefer. (Try catching a bus
between scheduled routes and see how well your subjective perception works).
But if you're talking about
history, well that's not a physical quantity. It's just stories and facts and theories about events and what influenced them. History (I mean the human activity of study) depends on time, but time pays no regard to our study of history.
I reduce time to its natural properties. Included in those natural properties are people's perception of and determination by time
Our perception is a physical property of the thing perceived? That's like saying my reputation is somehow attached to my molecules.
Isn't this being-in-time primarily suffering?
Trees abide in time, and so do comatose patients. Do either suffer? I doubt it.
The suffering you're talking about is not a property of time, but a property of: a) our physical condition and b) the operation of our minds. The application of time to suffering is simply how it varies with respect to changes in everything else.
Does anyone believe in timelessness (a dimension of our existence where All of Time, rather than/or eternity, exists?
Someone might, but not me.

We know that our appreciation of time is largely a function of our minds, but the
application of time on us occurs anyway. We can create perceptions that
feel timeless, but we can also be hypnotised to enjoy the taste of cold pork lard. This says nothing more than that our perceptions are manipulable via our minds.
I note that people who 'meditate themselves into timelessness' don't manage to get vast amounts of constructive thinking done. This tells me that their minds are
reducing some function to produce this effect. (On the plus side, you can appreciate colours and other sensations more)
A sense that the future must exist, even if only in the imagination; or that we have no conceivable reason to see why the future will not exist. A sense that the past is still happening now, because, perhaps, of its irreversibility?
I'm not persuaded that the future exists - except in a story sense; and there are many stories. The past is discernible mainly because time and motion tend to be orderly. There's no reasonable doubt that the past
did exist, and there's fairly strong agreement in most cases as to what it was - but that's not an argument that it
does exist.
What does the lack of God mean for eternity, philosophically?
From my perspective, lack of god and lack of eternity point to the same thing: that we're inventing language for ideas we can't define constructively, can't identify physically and can't really use, except for pacification and social manipulation.