What is the poem that compare woman to a day?

The poem you're referring to is most likely "When I Consider How My Light is Spent" by English poet John Milton. Although not strictly comparing a woman to a day, here are the relevant lines from this sonnet about the poet comparing his own fading eyesight - here likened to the fading evening light - to "that one Talent", referring to the parable of the Ten Talents:

_When I consider how my light is spent,_

_Ere half my days, in this dark world and wide,_

_And that one Talent which is death to hide,_

_Lodged with me useless, though my Soul more bent_

_To serve therewith my Maker, and present_

_My true account, lest he returning chide;_

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