In a former article I’ve talked about the commands cron and crontab that are the standard way to schedule recurring things on a Gnu/Linux system. But sometimes you need to do one thing at a specific date and time for just one time, and for these tasks the best option is to use at, another way to use at is to run a command later when the computer won’t be busy. Or another reason could be that you want to run a command that requires a lot of time to end and you have to disconnect from that server, at could be used in this situation, but for these task i suggest to take a look at the articles on how to run commands on background and the utility screen