| Quote #1
a course of a river that turns, moves on,
Time is definitely not linear in "Piedra de sol"—this river that opens the poem is a good metaphor for the way time works for the speaker. It goes out, comes back, and is always arriving, just like how the speaker goes back into time and comes back, and his memories are always arriving in his brain.
| Quote #2
there's no one here, and the day falls,
Time often seems to be almost meaningless in this poem. Whether a day, a year, or a moment, nothing has much of an effect on the speaker's experience. This might be because he's already dead, or because time lost its meaning when he lost his lover. It's all the same to this dude.
| Quote #3
I search for an instant alive as a bird,
Even while time whooshes past him (yes, time whooshes), the speaker is desperately trying to pin down an instant, a particular moment in time. And it's just as tough as grabbing at dollar bills in a wind machine.