Debianhelp has published a new guide about scheduling Backup Jobs using at and crontab

You can schedule a command or a script using two tools

crontab : Schedules tasks once or repeatedly.

You can use the crontab command to run commands at regular times. For example, you could schedule a backup of your files every Friday. Commands can be scheduled to the minute.

at : Schedules tasks once.

You can use the at command to schedule a command or script to run a single time. The command includes several utilities

Scheduling Backup Jobs using at and crontab