Working on top of Keith's answer to suit your needs:
timeout /t X ; psexec -i -s Y
Where
timeout replaces sleep in Windows 7.
X is the seconds to wait defined by /t, add /nobreak if you want to disallow the user to continue.
psexec from Microsoft SysInternals allows you to run interactive (-i) as the local system (-s),
please note that you have to start psexec once to accept the first time EULA, or add -accepteula.
Y is your command.
runas doesn't allow you to start as local system, that's why to use PsTools for process-related tasks.
Starting a Scheduled Task or Service seems like too much of a workaround for me...
For example, Patrick's answer can simply be rewritten as:
timeout /t 120 ; psexec -i -s calc.exe