Is there a way to reduce lighting period on Red Sea 90s reef lights?

[Sunny in Miami]

I am trying to reduce the number of hours my lights are on. It seems that the program is set for 12 hour long photo period and when I try to reduce this the program won't let me.

 

[DanyL]

What do you mean by “the program won’t let me”?

Are you making sure you’re saving the changes?