What I've done so far.

[Bruce Leyland-Jones]

That's exactly what mine does. Why is mine potentially harmful for fish but yours isn't?

Mine doesn't give 20 hours of light.

 

[PADogman]

Mine doesn't give 20 hours of light.

Ah. Mine must have longer cycles of sunrise/set, moonlight and such.
Without watching it for 24 hours straight I am just guessing the complete darkness is four hours in a row, but it could be six. I know I can make a custom program if I need to change something, but it means choosing my reds, whites and blues intensity. And that is out of my wheelhouse.

 

[Bruce Leyland-Jones]

Ah. Mine must have longer cycles of sunrise/set, moonlight and such.
Without watching it for 24 hours straight I am just guessing the complete darkness is four hours in a row, but it could be six. I know I can make a custom program if I need to change something, but it means choosing my reds, whites and blues intensity. And that is out of my wheelhouse.

One of the attractions of my piece of kit was the ease of programming...and that's if I choose to do it all manually. Alternatively, can choose from some pre-set programs and, with each of these, adjust the timings.
Currently, 'sunrise' begins at 0830 and finishes setting by 2030. I then have some two hours of 'moonlight', before total lights out. I'm using a pre-set 'Plant Boost' program, for the spectrum side of things, although I'll be changing that when my stocking is complete in a week's time or so.

 

[PADogman]

One of the attractions of my piece of kit was the ease of programming...and that's if I choose to do it all manually. Alternatively, can choose from some pre-set programs and, with each of these, adjust the timings.
Currently, 'sunrise' begins at 0830 and finishes setting by 2030. I then have some two hours of 'moonlight', before total lights out. I'm using a pre-set 'Plant Boost' program, for the spectrum side of things, although I'll be changing that when my stocking is complete in a week's time or so.

That sounds nice.
I've read 50/50 reviews on mine. Some guys say it works perfect for them with the factory settings in their planted tanks, some say they made a custom program. Some say the light stinks.
But like I said in my OP, I needed something and this is what the shop sold me

Time will tell

 

[Bruce Leyland-Jones]

That sounds nice.
I've read 50/50 reviews on mine. Some guys say it works perfect for them with the factory settings in their planted tanks, some say they made a custom program. Some say the light stinks.
But like I said in my OP, I needed something and this is what the shop sold me

Time will tell

Once Upon A Time...they used candles for both light AND heat. We don't do so bad.