You would still need the Create task to make sure it is there on new machines. I would change the schedule to be what you want it to be. Then create a second Task to Update the named task (same name) to change the schedule. In the end, you will need two tasks in this. Your other option is to create a Delete task and remove it from your machines completely. Once you are sure this is done, create a new Create Task with the correct schedule and you will get the thing created (best with a different name) once any time a machine first enforces that policy. In this way you will only have one Task in your GPO.
Justin