S. R. Faruqi:

In this 'ground', a verse of Sauda's is almost an exact counterpart of Mir's:

thā bah javānī fikr-o-taraddud baʿd az pīrī pāyā chain
rāt to kāṭī dukh sukh hī meñ ṣubḥ huʾī ārām kiyā

[in youth, there was concern and anxiety; afterward, in old age, we found peace
we spent the night in ups and downs; when morning came, we rested]

Mir's verse is better because pīrī meñ līñ āñkheñ mūñd has a more appropriate affinity with ārām kiyā in the second line than does baʿd az pīrī pāyā chain . Then, the metaphor rāt bahut the jāge is better than the flat account rāt to kāṭī dukh sukh meñ . The colloquialness of dukh sukh is more appropriate for zindagī than for rāt . Then, rāt jāgnā in any case suggests the spending of the whole night in misery.

Between 'youth' and 'night', and 'old age' and 'morning', the affinity is obvious. Because in youth the hair is black, and in old age white.

Another point is that youth is generally construed as day, and old age is generally construed as evening or night. The poet has used them quite contrarily to this, through which a new pleasure has been created.

[See also {543,1}.]

FWP:

SETS == OPPOSITES
MOTIFS == NIGHT/DAY
NAMES
TERMS == AFFINITY

SRF's point about the color-coding is exactly right: the imagery here completely reverses our expectations. And it does so with such an air of simplicity and obviousness that it takes a minute even to realize the reversal. The verse sounds matter-of-fact and neutral: the speaker is simply giving us a brief overview of his life-- in the first line literally, and in the second line through a clearly framed metaphor. The unusualness of it only hits us afterwards. This is a fine verse to reflect on as you grow older.

Mir plays a variant of the same trick in

{1567,2},

where he associates a rosebud with autumn.

The yaʿni seems to equate being wakeful with weeping; there's apparently no other youthful activity available except the shedding of tears.

Compare Ghalib's treatment of the candle, which burns all night and can only 'rest' at dawn, when it's burnt out:

G{78,7}.