using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        DateTime dt = DateTime.Today;

        Console.WriteLine(System.Text.Json.JsonSerializer.Serialize(dt));

        dt = System.Text.Json.JsonSerializer.Deserialize<DateTime>(System.Text.Json.JsonSerializer.Serialize(dt));

        Console.WriteLine(dt.Year);

        var o = new System.Text.Json.JsonSerializerOptions();

        o.NumberHandling = System.Text.Json.Serialization.JsonNumberHandling.AllowReadingFromString;

        string json = "{\"time\": \"99999000\"}";

        var test = System.Text.Json.JsonSerializer.Deserialize<Test>(json, o);

        Console.WriteLine(test.time);

    }

}

​

public class Test

{

    public long time {get; set;}    

}