S. R. Faruqi:

Just before dawn, in the sky a single white line of light is apparent (which is mentioned in the Qur'an too, where the simile of a white thread has been given for it). Since this white line seems to be dividing the sky vertically [ʿamūdī t̤aur par], the simile of 'the tearing of the collar' [chāk-e garebān] is given for it (because the tearing of the collar too is vertical, and makes a line on the clothing). In this regard the dawn is called 'the tearing of the collar'.

Now let's consider the meaning of the verse. He has called himself 'collar-tearing'-- that is he hasn't declared himself to be the bearer of any special news/event. The tearing of the collar is the first stage of madness. Thus it's not the bearer of any special news/event. But then he's said that the dawn too is 'collar-tearing'. Thus he has established a presumption about his own news/event-- that is, we are not less than the dawn.

Now he's said that the interval/leisure was so little that in it no more accomplishment can be achieved, than that the collar would be torn. Since the dawn too remains only for a little while (that is, when the day advances, then we don't call it dawn), there's an affinity between the little interval/leisure of a lifetime, and the dawn.

In the second line, the interrogative style too is very enjoyable. There's of course the implication that the interval of a lifetime is small; there's also the suggestion that if the interval had been greater, then perhaps some other tasks (that is, other tasks in addition to passion) would have been possible. Now, when the interval itself is very short, it's enough that we would tear our collar.

In the first line, there's also the interpretation that collar-tearing can be of different kinds, but if we adopt a kind of collar-tearing like that of the dawn, then that's plenty good enough. Now the possibility has been created that perhaps some styles of collar-tearing might be better than the collar-tearing of dawn. Or again, the dawn's collar-tearing might be the best of all.

In the verse there's a strange kind of lamentation; but the style is one of carelessness and a touch of arrogance-- but also of melancholy. A person can do a great deal, but he's been given little time. Nevertheless, despite this lack of time, what he has done is not commonplace or of poor quality. A person may be helpless in a thousand ways, but he's not of little value. Collar-tearing is not only a metaphor for passion; rather, it's a symbol for a whole style of life and the whole human inquiry into it. He's composed a powerful verse.

FWP:

SETS == HI; KYA
MOTIFS == CHAK-E GAREBAN
NAMES
TERMS

Just look at the range of readings (thanks to the hī ) for hai bahut jeb-chākī hī :

(1) 'Collar-tearing itself is plenty much, it's enough.' (SRF's reading)
(2) 'There's much collar-tearing [going on]!' (Reading hī as 'emphatically'; we must figure out the significance of this emphasis)
(3) 'There's nothing except a lot of collar-tearing [going on].' (Reading hī as 'only')

My translation follows SRF's reading, but I can't see any reason to rule out the other readings. For since collar-tearing is a sign of grief, it could quite well be taken as a show of grief over the smallness of the interval of human life. By no coincidence, all these readings also work well with the second line.

Moreover, thanks to the 'kya effect', the second line brings along its own set of possibilities:

='What could be done...!' (a lot could be done; an exclamation of admiration for the possibility)
='As if anything could be done...!' (of course it can't; an exclamation of scornful indignation)
='Could anything be done...?' (a question; the speaker is unsure)

On the nature of collar-tearing in relation to the 'crack of dawn', see G{67,1}.