iphone - カウントダウンタイマーが正確ではない

Question

アプリで真夜中までカウントダウンしています。唯一の問題は、カウントダウン タイマーが常に 5 分以上ずれていることです。真夜中までの実際の残り時間を本当に閉じることはありません。私は計算を行い、それが正しいと確信していますが、愚かな間違いを犯している可能性があります.

-(void) timerRun
{
NSDateFormatter *formatterAmPm = [[NSDateFormatter alloc] init];
[formatterAmPm setTimeZone:[NSTimeZone timeZoneWithName:@"America/New_York"]];
[formatterAmPm setDateFormat:@"a"];

NSString *amPmString = [formatterAmPm stringFromDate:[NSDate date]];

secondsCount = secondsCount + 1;
int hours = ((12*3600)-(secondsCount))/3600;
int minutes = ((12*3600)-(secondsCount)-(hours*3600))/60;
int seconds = ((12*3600)-(secondsCount)-(hours*3600))%60;

NSString *timerOutput = [NSString stringWithFormat:@"%.2d:%.2d:%.2d", hours, minutes, seconds];
_countDownLabel.text = timerOutput;

if ((secondsCount == 0) && ([amPmString isEqualToString:@"AM"]))
{
    [_countdownTimer invalidate];
    _countdownTimer = nil;
    MainViewController *ViewController = [[MainViewController alloc] initWithNibName:@"MainViewController" bundle:nil];
    ViewController.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
    [self.navigationController pushViewController:ViewController animated:YES];
    self.sidePanelController.centerPanel = [[UINavigationController alloc] initWithRootViewController:[[MainViewController alloc] init]];

}
}

-(void) setTimer
{
NSDateFormatter *formatterHour = [[NSDateFormatter alloc] init];
[formatterHour setTimeZone:[NSTimeZone timeZoneWithName:@"America/New_York"]];
[formatterHour setDateFormat:@"HH"];

NSDateFormatter *formatterMinute = [[NSDateFormatter alloc] init];
[formatterMinute setTimeZone:[NSTimeZone timeZoneWithName:@"America/New_York"]];
[formatterMinute setDateFormat:@"mm"];

NSDateFormatter *formatterSecond = [[NSDateFormatter alloc] init];
[formatterSecond setTimeZone:[NSTimeZone timeZoneWithName:@"America/New_York"]];
[formatterSecond setDateFormat:@"ss"];

NSDateFormatter *formatterAmPm = [[NSDateFormatter alloc] init];
[formatterAmPm setTimeZone:[NSTimeZone timeZoneWithName:@"America/New_York"]];
[formatterAmPm setDateFormat:@"a"];

NSString *amPmString = [formatterAmPm stringFromDate:[NSDate date]];
NSString *hourString = [formatterHour stringFromDate:[NSDate date]];
NSString *minuteString = [formatterHour stringFromDate:[NSDate date]];
NSString *secondString = [formatterHour stringFromDate:[NSDate date]];

int hour = (([hourString intValue]) * 60 * 60);
int minute = (([minuteString intValue]) * 60);
int second = [secondString intValue];
if ([amPmString isEqualToString:@"PM"])
{
    stopTime = 12*60*60;
}
else
{
    stopTime = 24*60*60;
}

secondsCount = hour + minute + second;

secondsCount = secondsCount - stopTime;

_countdownTimer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self     selector:@selector(timerRun) userInfo:nil repeats:YES];
}