'Schedule code for later execution.
system:  an string identifying the hook to be executed
data:    passed to the hook as an argument
delay:   (optional) a datetime.timedelta indicating the desired
execution time'

@classmethod
def schedule(cls, system, data, delay=None):

    if (delay is None):
        delay = timedelta(minutes=60)
    key = (datetime.now(g.tz) + delay)
    scheduled = {key: data}
    cls._set_values(system, scheduled)
    return scheduled
