我这个办法可以,但不知道有没有更简单的
 public static string GetTime(string times)
        {
            string NewNum = "";
            StringBuilder Nums = new StringBuilder ();
            foreach (char c in times)
            {
                if (char.IsDigit(c))//如果是数字
                {
                    Nums.Append(c);
                }
            }
            NewNum =Nums.ToString();
            return NewNum;
            
        }
        static void Main(string[] args)
        {
            Console.WriteLine("请输入第一个时间:");
             string times_first = Console.ReadLine();
             int time1 = int.Parse(GetTime(times_first));
             Console.WriteLine("请输入第二个时间");
             string times_second = Console.ReadLine();
             int time2 = int.Parse(GetTime(times_second));
             if (time1 > time2)
             {
                 Console.WriteLine("第一个时间较长!");
             }
             else
             {
                 Console.WriteLine("第二个时间较长! ");
             }
            Console.ReadLine();
        }