Bruce,
Do you have a lot of rules running by the scheduler?
Do any of them run processes that might run a long time?
If both of those are true, it might be possible that the rule you are asking about does not execute between 8:00 and 8:01.
Have you checked the logs? Make sure you select "All server events excluding SQL" so that rules run by the scheduler are written to the logs.
If it makes sense, move the rule in question to be the first rule in the scheduler. It should run then.