using System;

using Newtonsoft.Json;

public class Program {

    public static void Main() {

        var t = new Thing { Id = Guid.NewGuid(), CollectionTime = TimeSpan.FromSeconds(5) };

        Console.WriteLine(JsonConvert.SerializeObject(t));

    }

}

​

public class Thing {

    public Guid Id { get; set; }

    public TimeSpan CollectionTime { get; set; }

}