A combination of enjambed and end-stopped lines sets the pace of the poem.
In the first stanza, for instance, the first three lines are enjambed, mirroring the idea that the speaker can't "delay" the metaphorical river of time. The poem sweeps along without slowing down, reflecting exactly what the speaker is saying: time stops for no one.
The next two lines end with images of water ("river," "waterfall"), and the enjambment here continues to support the idea of time flowing quickly past. The next three lines, however, go back and forth between being end-stopped and enjambed:
[...] minute by glinting minute,
all that I have and all I am always losing
as sunlight lights each drop fast, fast falling.
The first end-stop here—a gentle comma—slows down the rush of enjambments, suggesting that the speaker has paused to get a good look at her life as a whole. But the enjambment in line 5 reminds readers of the speaker's big insight: people can pause to consider, but time always flows on, and eventually takes everything away. Finally, line 6 is end-stopped, suggesting the finality of death. (In fact each stanza concludes with an end-stopped line, bringing the speaker back to a firm "ending" over and over.)
Overall, the poem's mixture of enjambments and end-stopped lines suggests that, though the speaker can do nothing to slow time down, she can at least learn to appreciate the beauty of what's in front of her before it's gone.