实现代码:

#pragma mark - timeClick
- (void)timeClick:(UIButton *)btn
{
    long testTime = [ _timeTextFiled.text intValue];//定义一个长整形变量
    NSNumber *nsTime = [NSNumber numberWithLong:testTime];//将基本数据类型转换为NSNumber数据类型
    int hour = [nsTime intValue] / 3600;
    int minute = ([nsTime intValue] % 3600) / 60;
    int second = [nsTime intValue] % 60;
    if (hour < 10){
        if (minute < 10 && second >= 10){
            _timeLable.text = [NSString stringWithFormat:@"0%d:0%d:%d", hour, minute, second];
        }else if (minute < 10 && second < 10){
            _timeLable.text = [NSString stringWithFormat:@"0%d:0%d:0%d", hour, minute, second];
        }else if (minute >= 10 && second < 10) {
            _timeLable.text = [NSString stringWithFormat:@"0%d:%d:0%d", hour, minute, second];
        }else if (minute >= 10 && second >= 10){
            _timeLable.text = [NSString stringWithFormat:@"0%d:%d:%d", hour, minute, second];
        }
    }else {
        if (minute < 10 && second >= 10){
            _timeLable.text = [NSString stringWithFormat:@"%d:0%d:%d", hour, minute, second];
        }else if (minute < 10 && second < 10){
            _timeLable.text = [NSString stringWithFormat:@"%d:0%d:0%d", hour, minute, second];
        }else if (minute >= 10 && second < 10) {
            _timeLable.text = [NSString stringWithFormat:@"%d:%d:0%d", hour, minute, second];
        }else if (minute >= 10 && second >= 10){
            _timeLable.text = [NSString stringWithFormat:@"%d:%d:%d", hour, minute, second];
        }
    }
    //隐藏键盘
    [_timeTextFiled resignFirstResponder];
}

时间转换HH:MM:SS格式Demo