dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(10.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
    // TO DO METHOD CALL.
});

[[NSUserDefaults standardUserDefaults] setObject:[NSDate date] forKey:@"ReminderStart"]

NSCalendar *gregorianCalendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    NSDateComponents *components = [gregorianCalendar components:NSMinuteCalendarUnit
                                                        fromDate:REMINDER_START_DATE
                                                          toDate:[NSDate date]
                                                         options:0];
if (components.minute > 30){
   //call your method here if the time difference is larger than 30 minutes
}