Validate Time Fromat using C#

using System;

public class Program
{
      public static int checkCharacters (String n)
      {
          int val=0;
          int val1,val2,val3,val4,len;
          char [] charattay=n.ToCharArray();
          val1= (int)charattay[0];
          val2=(int)charattay[1];
          val3=(int) charattay[3];
          val4=(int)charattay[4];
          len=n.Length;
          if((len==8) && (val1>=48 && val1<=57) && (val2>=48 && val2<=57) &&
          (charattay[2]==':') && ( val3 >=48 && val3 <=53 ) && (val4>=48 && val4<=57) &&
          (charattay[6]=='p' || charattay[6]=='P' || charattay[6]=='a' || charattay[6]=='A') &&
          (charattay[7]=='m' || charattay[7]=='M'))
          {
             val=1;
          }
          else
          {
             val=-1;
          }
          return val;
       }
   public static void Main()
   {
       int value;
       String n;
       Console.WriteLine("Enter your Time:");
       n=Console.ReadLine();
       value=checkCharacters (n);
       if(value==1)
          Console.WriteLine("Valid Time");
       else
          Console.WriteLine("Invalid Time");

   }
}