It depends where you are on the "world".

Although it is a flat disk it is as though the sun is "South".
So the further North you go the days get shorter and the sun arcs lower in the sky in the Far North biome. Kind of funny watching the sun going yo-yo jumping between Black Forest and Far North.
In the south it turns night but really it seems when you are in Ashlands it is eternal day.

So length of daylight depends on biome you are in. At sea it gets light fairly close to the Day / Night cycle does it not? Not really timed it honestly per biome.