NSTime创建一个timeInterval

updateLabel2

timeLeft = [[NSDate date] timeIntervalSinceDate:[[NSUserDefaults standardUserDefaults] objectForKey:@"lastDate"]];

[[self timer] setText:[NSString stringWithFormat:@"Time Remaining: %f", timeLeft]]; //Set the label text

    [[NSUserDefaults standardUserDefaults] setObject:[NSDate date] forKey:@"lastDate"];


self.repeatTimer = [NSTimer scheduledTimerWithTimeInterval:1
                                               target:self
                                             selector:@selector(updateLabel2) 
                                             userInfo:nil
                                              repeats:YES];