To schedule a command or script to run at some particular time, the at command is perfect and provides many options for specifying the time you want it to run. It will set the task up to be run whenever you specify, and you can view the scheduled tasks or even change your mind and cancel one of them as you see fit.
The at command differs from cron in that it sets up a command or script to run only once, while cron allows you to set up commands or scripts to be run on a specified schedule – whether every day, once a week, a couple times a month or even just once a year.
at command syntax
Using the at command is relatively easy, though it has a lot of options, particularly on how you specify the time a task should be run. If you specify a time like shown below, the task will be set up to be run the next time you reach 15:27 (3:27 PM), whether that’s today or tomorrow.
Source:: Network World – Linux