get/set logonHours by using C# web api 2.0

I would like to enable/disable logonHours for particular user by using Web api 2.0 ,tried with code, everything is working fine set/get other than that logonHours, please help me out.

DirectoryEntry("LDAP://test.com","Administrator", "tesT.123$")) {

            using (DirectorySearcher objAdSearcher = new DirectorySearcher(objRootEntry))
            {
                objAdSearcher.Filter = "(&(objectClass=user)(samAccountName=" + username + "))";

                SearchResult objResult = objAdSearcher.FindOne();

                if (objResult != null)
                {
                   objResult.GetDirectoryEntry().Properties["title"].Value = "Test"; //its working fine.

                    byte[] logonHours = new byte[] { 0, 0, 0, 0, 0,0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,0, 0, 0, 0, 0 };
                    //byte[] logonHours = new byte[] {255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255 };
                    objResult.GetDirectoryEntry().Properties["logonHours"].Value = logonHours; //its not working, also not throwing any error
                    objResult.GetDirectoryEntry().CommitChanges();


                }
            }
        }

Thanks in advance