There would be some excellent reasons for launching a night assault. If towers have less range it would be the best time to lay siege, especially if there is no treb type unit that outranges all defenses. As well, if los is reduced that would be great for attacking an enemy town as defending units would not respond as well, while your units are not as affected since they would be in mass and sitting right next to tc's, barracks, etc. And of course if you had a melee heavy army night would be the best time to engage a missile heavy force, the reduced missile range would be a big help. And cav raiders would find it handy since defending halb type units would soon lose los when pursuing, allowing the cav to quickly get back to work killing the defender's econ.
But I can see why ES decided against day/night cycles in rm, it would mean even more balance tweaking and tuning. Day/night would open up potential exploits players could use that might unbalance the game.
Little_Wing
Oh as I was young and easy in the mercy of his means,
Time held me green and dying
Though I sang in my chains like the sea.