Has this been running ok and just started to act up or is this the first execution of the tasks?
Have you verified time zones on your server?
Just in case this task is corrupted I would create a new one to kick off at some time and then verify that it started at ran at that time. Just to try to narrow down the issue.
The only time that I have run into issues with tasks not running at the scheduled time had to do with the setting for daylight savings time. But that only threw it off an hour. It didn't stop the task from running at all.
I gather from your description that there is no evidence that the job actually tried to run and failed?