Tafsir of Al-Lail 92:2

"And the day when it manifests" means it appears by the departure of the darkness of the night, or it becomes distinct and uncovered by the rising of the sun.

The first interpretation is based on the assumption that the "covered one" [in the previous verse] is the day, or everything that conceals, since the result of both is the consideration of the existence of darkness. The second interpretation is based on the assumption that [the covered one] is the sun, since the result of this is the consideration of its setting; thus, the parallelism between the two paired counterparts is improved thereby. The difference between the two verbs—being in the past tense [for the night] and the future/present tense [for the day]—has already been discussed.

Abdullah ibn Ubayd ibn Umayr read it as tatajalla (with two tas), with the pronoun referring to the sun. It was also read as tujliya (with the ta dammah and the jim sukoon), with the pronoun likewise referring to it [the sun].