You can use the at command to schedule any action, including running the commands detailed in that question.

For example, if you want to hibernate in 30 minutes:

echo 'pmi action hibernate' | at now + 30 min

Or if you want to suspend at 11:00 pm:

echo 'pmi action suspend' | at 11pm

If you need to run a command as root, run at with sudo rather than the command itself with sudo (since sudo should only be run interactively, unless you've configured it not to ask for your password). For example, the equivalents of the above commands using pm-hibernate and pm-suspend are:

echo pm-hibernate | sudo at now + 30 min

echo pm-suspend | sudo at 11pm