Above ground spawning of slimes is different from slime chunk spawning.
Underground there is no light level needed. Above ground they obey the rules of a regular mob.
the no moon is no slimes, but from the phase after to a full moon the spawning gets more. Full moon being the most liable spawning. Since they require the same light level as other hostile mobs, you will get a mix most of the time. The ratio will go up during a full moon, and most likely you will run across them in those hours of the night.
Slime chunks are still probably the best to farm them though, as they don't have light requirements like the surface ones do. Don't know if the moon affects the slime chunk spawned ones... As I have not made a slime farm since the change. Have ran into slimes on the surface during a full moon though.:)