Instead of holes in light mask
Mask pcb has soldermask and transparent windows

//

Holed on light mask shaped like the moon phase so they project on the front panel 

Or a small motor with a rotating pcb of the cycles 
With them very close against the back of the front panel

Or somehow other stuck on solid moon shaped on the back of the front panel

Or copper shapes on the back of a semi transparent front panel that get revealed when a light shines on it
Like a little blank circle that turns into a sillouhete of the moon

^ tried that it didn't really work