Local notification - sample app

[fast]

hi,
I would add to the local notification to my app that iOS 5
displays a simple text to be displayed by the hour
targets (6AM, 12AM, 6PM, 12PM)
I created this code but no good, because it at intervals and not
predetermined hours, can anyone help?

- (void)applicationDidEnterBackground:(UIApplication *)application{


        NSDate *alertTime = [[NSDate date] dateByAddingTimeInterval:10];

        UIApplication* app = [UIApplication sharedApplication];

        UILocalNotification* notifyAlarm = [[UILocalNotification alloc] init];

        if (notifyAlarm) {

            notifyAlarm.fireDate = alertTime;

            notifyAlarm.timeZone = [NSTimeZone defaultTimeZone];

            notifyAlarm.repeatInterval = (360*60);

            notifyAlarm.soundName = @"suono tasto8.caf";

            notifyAlarm.alertBody = @"Hello universe!";



            notifyAlarm.applicationIconBadgeNumber = NO;           


            [app scheduleLocalNotification:notifyAlarm];


        }
}