I don’t think I’d want there to be nighttime. Maybe just a morning-to-sunset cycle, or maybe to-twilight, but even that might be too dark for me. And if implemented, a way to shut it off/not have it, of course.
How about just the ability to set the time of day for a map at the start of a match (no cycles)? Actually, this might be my ultimate preference, since the thought of day/night cycles or the passage of time during a match (even just visually) doesn’t do much for me from a gameplay or visual perspective. Being able to set the time of day, however, gives one more layer of visual uniqueness that a map could have without going into full-fledged cycles or time shifts and related impacts to unit power/speed. Tall vs. short shadows, color hue variations, etc. could be achieved through a time of day setting.
Age of Mythology had an Eclipse power to cast a shadow over the map for a short length of time. The thought of something like that happening on an AoE map for 5, 10 or 20 minutes at a time as part of a cyclical time cycle does not sound fun to me.