4.4.1. Use that idle time!
A Linux system can have a lot to suffer from, but it usually suffers only during office hours. Whether in an office environment, a server room or at home, most Linux systems are just idling away during the morning, the evening, the nights and weekends. Using this idle time can be a lot cheaper than buying those machines you'd absolutely need if you want everything done at the same time.
There are three types of delayed execution:
Waiting a little while and then resuming job execution, using the sleep command. Execution time depends on the system time at the moment of submission.
Running a command at a specified time, using the at command. Execution of the job(s) depends on system time, not the time of submission.
Regularly running a command on a monthly, weekly, daily or hourly basis, using the cron facilities.
The following sections discuss each possibility.