using System;

using System.Linq;

using System.Text.RegularExpressions;

public class Program

{

    public void Main()

    {

         var searchInput = "Field1:val1,Field2:val2,Field3:val3,Field4:2013-12-11T01:00:00";

         var regex = new Regex(@"(?<key>\w*)[:](?<value>[\w-:]*),?");

         var matches = regex.Matches(searchInput);

​

        var pairs = from Match match in matches

        select new {Key = match.Groups["key"].Value, Value = DateOrString(match.Groups["value"].Value)};

​

        foreach (var pair in pairs)

        {

            Console.WriteLine("Key: {0} Value: {1}",pair.Key,pair.Value);

        }

    }

    public static object DateOrString(string input)

    {

        if (String.IsNullOrWhiteSpace(input))

            return input;

        DateTime parsedDate;

        if (DateTime.TryParse(input, out parsedDate))

            return parsedDate;

        return input;

    }

}