The Overworld Lunar Cycle is based on the circulation of the primary moon that orbits around the planet. The moon orbits at a somewhat quick rate in comparison to the moon that those of Earth Clone are used to. A complete cycle occurs in close to 20 days. Let's consider a New Moon day one.
New Moon - Day 1
Incre Mina
First Quarter - Day 6
Incre Maxa
Full Moon - Day 10
Decre Maxa
Last Quarter - Day 15
Decre Mina
New Moon - Day 21