I like to know also. I think what you see in sky is affected by air quality particles at the time. I have no idea what it looks like under water.
Personally when had the chance to snorkel I avoided sun rise and sun set. (That's Jaws feeding time on the reef).
Seen to many reports of missing surfers out at dusk in the news.
Since moving to LEDs I now ramp up both color (Blue - White about 20K to 14/12K) and intensity (10 to 55% on LED) Same for ramp down.
In theory it gives the coral time to wake up before LED and T5 are full intensity of the lighting. Don't know if that's true or not.
Not sure if ramping color also has benefit or not. Looks cool though. Ohh that glow that LED glow.