After the fall of the Lamps, Yavanna decreed that most of the living things in Arda should sleep until light returned. She then gathered up the available light and made the Two Trees to illuminate Valinor.
The Sleep of Yavanna ended with the first rising of the Sun and Moon; but this happened only because Ungoliant killed the Two Trees, which surely was not in Yavanna's plan.
So, if not for Ungoliant, how did Yavanna (or the Valar in general) intend for the Sleep to end?