using System;

​

public class Program

{

    public static void Main()

    {

        TimeZoneInfo easternZone = TimeZoneInfo.FindSystemTimeZoneById("America/Toronto");

        var diffDay = new DateTime(2021, 10, 20, 2, 0, 0, DateTimeKind.Utc);

        var sameDay = new DateTime(2021, 10, 20, 22, 0, 0, DateTimeKind.Utc);

        var estDiffDay = TimeZoneInfo.ConvertTimeFromUtc(diffDay, easternZone);

        var estSameDay = TimeZoneInfo.ConvertTimeFromUtc(sameDay, easternZone);

        var estDiffDayStart = estDiffDay.AddDays(-1).Date;

        var estSameDayStart = estSameDay.AddDays(-1).Date;

        var estDiffDayEnd = estDiffDayStart.AddDays(2).AddTicks(-1);

        var estSameDayEnd = estSameDayStart.AddDays(2).AddTicks(-1);

        Console.WriteLine($"UTC Start:(Diff) {diffDay}, (Same) {sameDay}");

        Console.WriteLine($"EST Start:(Diff) {estDiffDay}, (Same) {estSameDay}");

        Console.WriteLine($"EST Range:(Diff) {estDiffDayStart} - {estDiffDayEnd}, (Same) {estSameDayStart} - {estSameDayEnd}");

    }

}