In your Task Schedule, do you have 'Enable randomization' set?
BTW it's a good idea to have randomization to save all your updates hammering the server at the same moment. I have mine set to 45 mins, which means that if I have a task time of 07:10, the client may decide to update anytime from then until 07:55. It keeps things within an hour, but does spread the load.
Do you have 'Run missed task' set to on? If so, then the missed task may run at any time.
A couple of things to check....