using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

     var lista = new List<MyObject>();

            lista.Add(new MyObject { Description = "123" });

            lista.Add(new MyObject { Description = "456" });

            lista.Add(new MyObject { Description = "678" });

​

            IEnumerable<MyObject> returnn = lista.Where(p => p.MinDate.HasValue && p.MaxDate.HasValue).ToList();

        Console.WriteLine(returnn.Count());

    }

   class MyObject

    {

        public DateTime? MinDate { get; set; }

        public DateTime? MaxDate { get; set; }

        public string Description { get; set; }      

​

    }

}