- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    [application setMinimumBackgroundFetchInterval:UIApplicationBackgroundFetchIntervalMinimum];//default fetch interval is never,

    return YES;
}

Target->Capabilities->backgroundModes->backgroundFetch

-(void)application:(UIApplication *)application performFetchWithCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler

+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)ti
                                     target:(id)aTarget
                                   selector:(SEL)aSelector
                                   userInfo:(id)userInfo
                                    repeats:(BOOL)yesOrNo;