Use rtcwake to "wake up" from sleep mode at a given time

Note that if you try this whilst in X, your laptop/pc will resume with X garbled. Therefore go into another Ubuntu session and execute the commands.

# Login to another session
CTRL + ALT + F1

# Put laptop to sleep and automatically resume after 10 seconds
sudo rtcwake -m mem -u -v -s 10

# After resume from sleep go back to original xsession
CTRL + ALT + F7