In the myth, Cupid only comes to Psyche in the dark, so she doesn't know who he is or what he looks like. What's Cupid's motivation for hiding his identity? Was he planning to do that indefinitely if Psyche hadn't disobeyed his order and took a peek at his face?
Cupid hides himself because he is a god, and also because he was ordered by Venus to kill Psyche but instead falls in love with her. So to shield his identity and his true self from Psyche, he only appears in the dark so that she doesn't see the true majesty that he is and so that the message would not get back to Venus who is his mother that he in fact betrayed her trust and orders by not killing Psyche.
It's a test. Cupid is the heart, Psyche is the mind. The story is about trusting your emotions over your reason (or gossip, or relatives, come to that) when it comes to love/marriage. He wanted her to trust him (to trust in her emotions) until he was satisfied that she was loyal to him and not her birth family, or until she proved that she had conquered her own doubts and would obey her husband (appalling now, but an appropriate sentiment at the time).
Tests in Greek mythology are not indefinite, although Psyche fails this one without the terms ever being announced, so we don't know how long it might have gone. In mythological terms, "until she fell in love with him" is probably a good rough deadline. She would have had to fake it ’til she made it, so to speak.