I'm a big fan of Flux, I feel better when I'm going to sleep since I used it. But I think this software can be more awesome to use. I think it would be great if we can set the hours of working (like Night Shift on iOS 9). I don't always want it to start changing the color temperature right after the sun sets.
An other option could use the luminosity sensor available on compatible macs (there is plenty of them) to yellow when we are in dark room (again setting the light level would be great).
Tell me what you think of this, I'm curious to know your opinion.
What version are you using on Mac OS? Maybe you need an update? You can set your wake time and many custom hours.
We don't offer customizable hours in the way you're requesting, because the nightly melatonin cycle is long and interrupted by bright light. Dimming screens and house lights starting a couple of hours before your normal sleep time is generally recommended.