Use notification in Ubuntu

Use crontab and notify-send:

EDITOR=gedit crontab -e

Add schedule:

15 12 * * 1-5 DISPLAY=:0.0 notify-send --urgency normal -i typing-monitor “Lunch” “Lunch”
15 17 * * 1-5 DISPLAY=:0.0 notify-send --urgency normal -i ktip “End of work day” “go home”

Save and close.