Night Blooming Cereus at Night

My cereus montrosa aka Peruvian apple cactus

continues to bloom with a flourish. It now combines many blossoms with the apples.

Therefore attracting the birds and the bees and the bats.

The blossoms are wide open at night, from dark to early dawn. By daylight the blooms are starting to shrink.

I don't know what the biology is behind the night blooming. Help me wikipedia. It is difficult to shoot at night because the view finder is dark. What the pros do is set up a try pod while it is still light and then take the photo after dark.