Install bbtime by entering the following commands in the terminal:
sudo apt update sudo apt install bbtime
Time tool for the blackbox/fluxbox window managers
bbtime is a blackbox tool to display the system time in your blackbox slit. It can also display other times as an offset of your local time in a menu. . Note that you don't actually need blackbox or fluxbox for this program to work, but it won't look as good in other window managers.