If you find you are using commands like sleep to run a one-off task at a specific time, then meet the GNU at command.
at will allow you to specify a time to run a specific command, and accepts a wide range of different formats including “now + 4 hours”, “noon”, and “next tuesday”. The command will read commands from stdin or using the -f to specifiy a file to be executed using the default /bin/sh.
One can find a great summary of the command’s use and available formats for time specification at the link here.
Once a job has been scheduled, the list of pending jobs can be listed with atq, and a job can be removed with atrm followed by a job ID.