I would say that moving at night, when the Nazgul are strongest, would have been more likely to attract their attention.
When you are hiding at night, you are still in a world where most things (at least humans and hobbits) are still. At night the senses of the Nazgul are as sharply focused as they ever are, and their powers of fear and terror are greatest.
During the day, travellers normally move, hunters hunt, rangers range
, and there is all manner of movement in the wilderness. So if you move during the day, at least you don't call so much attention to yourself by doing so.
Just my $.02, probably worth exactly what you paid to read it.
