to get you started, here's an example
Start by typing 'at' followed by what time a certain command should be executed:
$ at 14:00
at>echo "Hello" > /dev/ttyX
This will make "Hello" appear on the screen (your tty)
type ctrl+d to exit:
at>(ctrl+D)
job 6 at 2002-03-20 14:00
now you can type 'atq' to check your "ats"
$atq
6 2002-03-20 14:00 a user