te upetya mahā-rātre
tamasi pratyupasthite
urvaśyā uraṇau jahrur
nyastau rājani jāyayā
te - they, the Gandharvas; upetya - coming there; mahā-rātre - in the dead of night; tamasi - when the darkness; pratyupasthite - appeared; urvaśyā - by Urvaśī; uraṇau - two lambs; jahruḥ - stole; nyastau - given in charge; rājani - unto the King; jāyayā - by his wife, Urvaśī.
“The dead of night” refers to midnight. The mahā-niśā is described in this smṛti-mantra: mahā-niśā dve ghaṭike rātrer madhyama-yāmayoḥ, “Twelve o’clock midnight is called the dead of night.”