using System;

Test.LogRange(new DateOnly(2022, 9, 3));  // some random date

Console.WriteLine("start dst");

Test.LogRange(new DateOnly(2022, 3, 26));

Test.LogRange(new DateOnly(2022, 3, 27));

Test.LogRange(new DateOnly(2022, 3, 28));

Console.WriteLine("end dst");

Test.LogRange(new DateOnly(2022, 10, 29));

Test.LogRange(new DateOnly(2022, 10, 30));

Test.LogRange(new DateOnly(2022, 10, 31));

​

public static class Test

{

    public static DateTimeOffset NLDayToUTC(DateOnly day)

    {

        var ts = TimeZoneInfo.FindSystemTimeZoneById("Europe/Amsterdam"); // Hardcoded

        var date = new DateTimeOffset(day.Year,day.Month, day.Day, 0, 0, 0, ts.BaseUtcOffset);

​

        if (ts.IsDaylightSavingTime(date))

            date = new DateTimeOffset(date.DateTime, date.Offset.Add(TimeSpan.FromHours(1)));

        return date.ToUniversalTime().DateTime;

    }

    public static void LogRange(DateOnly day)

    {

        var start = NLDayToUTC(day);

        var end = NLDayToUTC(day.AddDays(1));

        var hours = (end-start).TotalHours;

        Console.WriteLine($"{day.ToString("yyy-MM-dd")} = {start.ToString("yyy-MM-dd HH:mm:ss zz")} - {end.ToString("yyy-MM-dd HH:mm:ss zz")} ({hours} hours)");

    }

}