How do I make the blue light filter on at all times?  

There is not a setting for this that I can find. The ONLY option for the blue light filter in Windows 10 is to set a schedule. I tried entering 12:00 AM for both the start and stop times, but that only leaves the blue light filter off at all times instead of on which does not make any sense to me. There is no checkmark for "always on" or anything like that. I am surprised that Microsoft did not include an option to leave it on at all times! Android already made that move. Perhaps I am missing something?

Is there a way to have it on at all times?

I have Update 1909 64-bit

Did you try 12:01 am to 11:59 pm?

Or some suitable time when you are not awake like 3:01 am to 2:59 am.

Hello Ornithophilia,

A quick way is to turn on or off Night light from the Action Center as you want.

Turn On or Off Night Light in Windows 10

You can turn it on and not set a schedule, but I found that didn't always stick. So I semi-tricked it with a schedule/

margrave55 said:

That blue light setting turns my screen an awful color. Intolerable.
Does it do that for you?

Kinda amber puke? It will if set too high. The gamma gets all fouled up. Takes just a little to give a mild grayish tint.

If the win32 apps like task manager, etc. had dark mode, I wouldn't use it at all.