Bedtime only engages when f.lux gets to the lowest point in the schedule - so clicking the button lets you "set it up" but not change to it, if that makes sense?
You can turn on the option to expand your slider ranges, and then you can adjust the "current" slider to a lower number as you like.
I have similar problem. I cannot access the controls for flux by clicking on the app. The app is running on its own and is way to dark and I cannot get to where I can make adjustments. I am using MacOS Catalina on a 2019 MacBook Pro 15".