def parse_hour_spec(hour_spec):
    """Hour spec is a two-hour time-window that dictates when an hourly backup
    should kick off.

    Ex. h_0000_0200 is a backup off that kicks off sometime between midnight
    and 2am GMT.
    """
    prefix, start_window, end_window = hour_spec.split('_')
    return int(start_window) / 100