Note: at is not installed by default on most of modern distributions.
To execute a job once at some other time than now, in this example 5pm, you can use
echo "somecommand &" | at 5pm
If you want to catch the output, you can do that in the usual way:
echo "somecommand > out.txt 2>err.txt &" | at 5pm
at understands many time formats, so you can also say
echo "somecommand &" | at now + 2 minutes echo "somecommand &" | at 17:00 echo "somecommand &" | at 17:00 Jul 7 echo "somecommand &" | at 4pm 12.03.17
If no year or date are given, it assumes the next time the time you specified occurs. So if you give a hour that already passed today, it will assume tomorrow, and if you give a month that already passed this year, it will assume next year.
This also works together with nohup like you would expect.
echo "nohup somecommand > out.txt 2>err.txt &" | at 5pm
There are some more commands to control timed jobs:
All commands apply to jobs of the user logged in. If logged in as root, system wide jobs are handled of course.