I have been one acquainted with the night (1 and 14)
This line introduces and concludes the verb tense of the poem, letting us know when it is happening – in the past. Perhaps the speaker is no longer acquainted with the night. The repetition of this phrase suggests that this poem takes place on not just one, but many nights. Also, the entire poem centers on a period of time – night time. The repetition of this line emphasizes the importance of the night.
I have walked out in rain – and back in rain. (2)
Though this line doesn't mention time specifically, it's an example of the repetition of the verb tense. This time the narrator has actually done something – walked – not just been something. So we start to get a sense of the poem's, and the speaker's, movement through space and time in this line. Also, this line deals with the length of time. The speaker has both walked out and back in rain, so it seems that he's talking about a pretty long, wet night.
One luminary clock against the sky
Proclaimed the time was neither wrong nor right (12-13)
In these lines, the idea of time plays a central role in the poem. These two lines intertwine with every theme of the poem: the moon is distant and isolated; the time the moon shows is dissatisfying; the similarity between a moon and a clock shows contrast between man and the natural world; and, of course the moon as clock is a vivid image of time. So, though the poem includes many themes, time runs through them all.