Melkor has to consider this question because how humans measure time here is different. Time has a strange meaning for a Valar who didn't yet know of the Sun and the Moon. It didn't help that he didn't need to sleep and so days held little meaning to him.

"I believe it's been a month now," he said thoughtfully. "I know a place near which sells something called French toast and bacon which is customary ate in the morning from what I can tell."