In Unix, use the AT command for a one-off schedule or the CRON tool for a repeating schedule.
In Windows, use the Windows Scheduler (available from the control panel).
In both, you have to know the syntax to run a SAS job in batch from the command line. Many Unix admins have written local scripts so batch jobs are easy to set up. In Windows, you have to put the options in yourself, so I usually develop the script in a Windows batch file (.bat extension) and then point the scheduler to the batch file.
My mainframe use is too rusty to give you pointers, beyond that it can be done there too.
As previously said, adding the task to the system scheduler would be the simplest and safest way.
But, if you wish to run your SAS program from a workstation and lets say, its a one time run only, I guess you could prepare a "special" datastep at the beginning of the program that will wait until the desired hour.
Something like this:
do until(datetime() gt '19APR2009 10:00:00'dt); /* check date/time */
call sleep(10,60); /* wait 10x60 seconds = 10mins until next check */