using System;

using System.Text.Json;             

​

public class Program

{

    public static void Main()

    {

        for(int i = 0; i < 1000; i++)

        {

            var date = DateTime.Now;

            var test = new Test() { Timetest = date };

            var stringdate = JsonSerializer.Serialize(test);

            Console.WriteLine(stringdate);          

        }

    }

    public class Test

    {

        public DateTime Timetest {get;set; }    

    }

}