countdown.sh [-f] <duration|-d date> [-q] [-t title] [-m message] [-e command]
-f Force execute. This option must be locate before <-d date>.
-q Quiet. Don't print message on exit.
-t title Show the title at the top of the screen.
-m message Show the message at the bottom of the screen.
-e command Execute command on timeup. The command will not be executed on cancel.
countdown.sh 30 # delay 30 seconds
countdown.sh 1:20:30 # delay 1 hour 20 minutes and 30 seconds
countdown.sh -d 23:30 # delay until 11:30 PM