using System;

using Newtonsoft.Json;

using Newtonsoft.Json.Converters;

public class Program

{

    public static void Main()

    {

        var jsonString =@"{""users"":[{""id"":1123,""last_update"":""2016-02-28 14:53:04""}],""page"":1,""pages"":1}";

        var obj = JsonConvert.DeserializeObject<Rootobject>(jsonString, 

            new IsoDateTimeConverter { DateTimeFormat = "yyyy-MM-dd HH:mm:ss" });

        Console.WriteLine(obj.users[0].last_update);

    }

}

​

public class Rootobject

{

    public User[] users { get; set; }

    public int page { get; set; }

    public int pages { get; set; }

}

​

public class User

{

    public int id { get; set; }

    public DateTime last_update { get; set; }

}