using System;

​

public class Program

{

    internal static readonly DateTime TimestampEpoch = new DateTime(1970, 1, 1, 0, 0, 0, 0, DateTimeKind.Utc);

    static long ToDurationSeconds(TimeSpan value, out int nanos)

    {

        nanos = (int)(((value.Ticks % TimeSpan.TicksPerSecond) * 1000000) / TimeSpan.TicksPerMillisecond);

        return value.Ticks / TimeSpan.TicksPerSecond;

    }

​

    public static void Main()

    {

        DateTime now = new DateTime(2019, 4, 1, 13, 0, 0, 0, DateTimeKind.Local);

        int nanos;

        var seconds = ToDurationSeconds(now - TimestampEpoch, out nanos);

        Console.WriteLine("{0}  {1}", seconds, nanos);

    }

}