Starting processes in the future

AT UTILITY

Eg
$ at now +3 days COMMAND

From the man-pages:

DESCRIPTION

at and batch read commands from standard input or a specified file which are to be executed at  later time, using /bin/sh.
at executes commands at a specified time.
atq lists the user's pending jobs, unless the user is the superuser; in that case,  everybody's  jobs  are  listed. The format of the output lines (one for each job) is: Job number, date, hour, queue, and username.
atrm deletes jobs, identified by their job number.
batch   executes commands when system load levels permit; in other words, when the load  average drops below 1.5, or the value specified in the invocation of atd.

CRON UTILITY

cron refers to a configuration file called /etc/crontab to execute a series of bash commands.

crontab -e opens the crontab editor to edit existing jobs or to create new jobs. Each line of the crontab file contains 6 fields.

FIELD - DESCRIPTION - VALUES
MIN - Minutes - 0 to 59
HOUR - Hour field - 0 to 23
DOM - Day of Month - 1-31
MON - Month field - 1-12
DOW - Day Of Week - 0-6 (0 = Sunday)
CMD - Command - Any command to be executed

* = All range of values

Example
0 08 10 06 * /home/sysadmin/full-backup.sh executes full-backup.sh at 8.30 a.m., 10-June, any day of the week

SLEEP COMMAND

From man page:

NAME
sleep - delay for a specified amount of time

SYNOPSIS
$ sleep NUMBER[SUFFIX]...
$ sleep OPTION

DESCRIPTION
Pause  for  NUMBER seconds.  SUFFIX may be 's' for seconds (the default), 'm' for minutes, 'h' for hours or 'd' for days. NUMBER need not be an integer. Given two or more arguments, pause for the amount of time specified by the sum of their values.