As mentionned in the article, each fireflies has a clock that drives when they decide to flash.

each firefly has its own individual internal clock

A clock in this case is like a counter, so we will start by adding a clock variable to our program.

and every time the clock “strikes twelve”, it flashes.

We can use a forever loop to repeat code that increments the clock.
When the clock reaches "noon" (let's pick 8), we turn on the NeoPixels briefly and turn them off to simulate a flash.