I didnt mean the duration of the sunset/sunrise was longer because of rotation nor by size of the planet. It just has to be different and "longer" since there is no "land" that covers the sun, so the sun just fades away slowly between the clouds untill you cant see it because you have too many clouds/gas or they are too dense to show it.

On earth the light disappears a few minutes after the sun has passed the horizon. Here, you dont have any horizon to cover the sun, so even when the sun is "under" the horizon you can still see it for a while, thats why its longer.

What i mean is that is not as inmediate as on a standard planet, there is no contrast between earth and sky, so the sun doesnt "set" just "fades". But ok, after a while there should be night.