using System;

public class Program

{

    public static void Main()

    {   

        DateTime specifiedTime = new DateTime(2017, 04, 02, 18, 51, 00);

        DateTime now = DateTime.Now;

        string timeName = null;

        try

        {

            // specify the TimeZone we're wanting to validate against

            TimeZoneInfo zone = TimeZoneInfo.FindSystemTimeZoneById("New Zealand Standard Time");

            // check whether the selected TimeZone is subject to Daylight Savings Time; assign correct name to the zone

            if (zone.IsDaylightSavingTime(specifiedTime))

            {

                timeName = zone.DaylightName;

            }

            else

            {

                timeName = zone.StandardName;

            }

            // convert specified time to UTC for comparison

            DateTime specifiedTimeAsUtc = TimeZoneInfo.ConvertTime(specifiedTime, zone, TimeZoneInfo.Local);            

            Console.WriteLine("Specified date/time converted to UTC for comparison:\r\n{0} {1} = {2} UTC.", specifiedTime, timeName, specifiedTimeAsUtc);

            // compare specified time in UTC to current DateTime in UTC, ascertain whether it falls before or after DateTime.Now

            Console.Write("Specified time in UTC compared to current Date/Time in UTC:\r\n");

            if (specifiedTimeAsUtc < now)

            {

                Console.Write("{0} < {1}\r\n", specifiedTimeAsUtc, now);

            }

            else if (specifiedTimeAsUtc == now)

            {

                Console.Write("{0} = {1}\r\n", specifiedTimeAsUtc, now);

            }

            else

            {

                Console.Write("{0} > {1}\r\n", specifiedTimeAsUtc, now);

            }

        }

        catch (TimeZoneNotFoundException tznfe) // typically a typo in row 14, TimeZoneInfo.FindSystemTimeZoneById()

        {

            Console.WriteLine(tznfe.Message);

        }                           

        catch (InvalidTimeZoneException itze) // this is thrown due corrupted Registry TimeZone data

        {

            Console.WriteLine(itze.Message);

        }

        finally

        {

            DisplayAllValidTimeZones();

        }

    }

    // get all TimeZone data stored in the Registry and display the Id for each as well as the base UTC offset we're using for comparison

    public static void DisplayAllValidTimeZones()

    {

        Console.WriteLine("\r\nALL VALID TIMEZONES FROM SYSTEM REGISTRY (with base UTC offset)\r\n");

        foreach (TimeZoneInfo z in TimeZoneInfo.GetSystemTimeZones())

        {

            Console.WriteLine("{0}, {1}", z.Id, z.BaseUtcOffset);

        }

    }

}