Trust me, you want Flux. Your eyes & sleep quality will thank you.
If you need to manually start the applet just type 'fluxgui' in terminal.
Resource: Flux Repo
sudo add-apt-repository ppa:nathan-renniewaldock/flux
sudo apt-get update
sudo apt-get install fluxgui
Resource: Create a Cron Task in Ubuntu
Check if cron is installed:
dpkg -l cron
Install cron (if needed)
sudo apt-get install cron
Verify cron is running.
systemctl status cron
Create a new cron job.
crontab -e
Select your terminal editor of choice.
Resource: Crontab Generator
Use the Crontab Generator to select when you want fluxgui to run. FYI: 'Command To Execute' field on Crontab Generator is 'fluxgui'
Verify cron job was created.
crontab -l
If you need to manually start the applet just type 'fluxgui' in terminal.
Winning! You're good to go.