Looking good.
I have been messing around with my lights today to make sure that everything is going to work as I want it to.
I bought 12v relays for switching them on/off but I had some issues with them. They suck a lot of power and caused some weird issues with the pwm signals from the pi. They seemed to cause the pwm signal to flicker.
I swapped them out for 5v and the flickering stopped. Not 100% sure if the flickering was cause by the increased voltage draw of the 12 v relays drawn straight from the pi hat 12v rail, but it may be something to consider when you pick relays for light control.
Since your going to set things up with the PCA 9685 you may not have the same issue. I'm running my relays straight from the pis GPIO pins.
Here's the lighting schedule I'm testing my lights with right now.
I have the timers for the blue channel set at 8AM to turn the relay on, then it ramps to a peak of 61% at 12PM then they ramp down to 8PM and the timer turns the channel off at 8PM.
The white channel relay turns on at 10AM and then ramps up to 45% at 2PM then ramps down till 8PM but the relay is set to shut off at 7:30PM.
This is just for testing the lights and may change once I see how the tank reacts.