There's a tiny little icon that appears on the bar across the top of your computer screen, to the left of the time. If you click there, you can set preferences, like "disable for full screen applications", or "disable for one hour". But you can also just plain quit out of f.lux when you don't want it on, and then start it up again by clicking on the icon in your dock or in your applications.
Yes we thought it was interesting (especially in the winter), that sleep timing dictates how much time you can spend outside when the sun is up. For some people it gets very small in the winter, so we put it in there.
Late 2018 Macbook 15" here; tried the build 39.9871 and the defaults write ... commands posted above. It largely works, but there are brief periods (< 5 seconds) where black parts of the screen show as bright cyan / bright blue, and then revert back to black. If it helps, I have the Intel UHD Graphics 630 card on this mac.
