I always have had problem with setting Night Light's active range on Ubuntu 20.04. The most obvious: 0h - 0h does not work. However setting 8h - 8h at 8.00 o'clock did work until today. Today it does not enable it and neither I can make it active with any kind of combination of time windows. I cannot see the graphical interface an option at all from now on, therefore I'm interested in:
If there is any command line alternative which can enable the Night Light permanently?
I'm not aware of any simple command line alternative, but you can keep Night Light on throughout the (24 hours) day using the Night Light Slider GNOME Shell extension. Its main purpose is to add a slider to the system menu to control Night Light's colour temperature:
But it also provides an option to enable Night Light all the time ('Enable always'):
This option actually periodically changes Night Light's schedule under the hood in order to keep it activated all the time.
P.S. Refer to this Q&A to learn about installing and managing GNOME Shell extensions: How do I install and manage GNOME Shell extensions?
