Install xfce4-time-out-plugin by entering the following commands in the terminal:
sudo apt update sudo apt install xfce4-time-out-plugin
Description:
time out plugin for the Xfce4 panel
This plugin makes it possible to take periodical breaks from the computer every X minutes. During breaks it locks your screen. It optionally allows you to postpone breaks for a certain time.
Homepage: http://goodies.xfce.org/projects/panel-plugins/xfce4-time-out-plugin
Version: 1.0.2-0ubuntu1
Section: universe/x11