US-centric, 99% accurate time zone helper.

TimeZoneHelper.cs

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine(new DateTimeOffset(DateTime.Now));
        foreach (var item in Enumerable.Range(1, 10))
        {
            var date = new DateTime(2018, 8, 16);
            var offset = TimeSpan.FromHours(-item);
            var now = new DateTimeOffset(date, offset);
            Console.WriteLine($"{now} = {TimeZoneHelper.DetermineZone(now)}");
        }
        Console.WriteLine(string.Empty);
        Console.Read();
    }
}

public static class TimeZoneHelper
{
    /*
        * Usage = var zone = DetermineZone(DateTime.Now);
        *
        * 8/16/2018 12:00:00 PM -01:00 = Unknown
        * 8/16/2018 12:00:00 PM -02:00 = Unknown
        * 8/16/2018 12:00:00 PM -03:00 = Unknown
        * 8/16/2018 12:00:00 PM -04:00 = Eastern
        * 8/16/2018 12:00:00 PM -05:00 = Central
        * 8/16/2018 12:00:00 PM -06:00 = Mountain
        * 8/16/2018 12:00:00 PM -07:00 = Pacific
        * 8/16/2018 12:00:00 PM -08:00 = Alaskan
        * 8/16/2018 12:00:00 PM -09:00 = Unknown
        * 8/16/2018 12:00:00 PM -10:00 = Hawaiian
        */

    public enum TimeZoneName
    {
        Hawaiian,
        Alaskan,
        Pacific,
        Mountain,
        Central,
        Eastern,
        Unknown
    }

    public static TimeZoneName DetermineZone(DateTimeOffset date)
    {
        if (TestOffset(TimeZoneName.Hawaiian)) return TimeZoneName.Hawaiian;
        else if (TestOffset(TimeZoneName.Alaskan)) return TimeZoneName.Alaskan;
        else if (TestOffset(TimeZoneName.Pacific)) return TimeZoneName.Pacific;
        else if (TestOffset(TimeZoneName.Mountain)) return TimeZoneName.Mountain;
        else if (TestOffset(TimeZoneName.Central)) return TimeZoneName.Central;
        else if (TestOffset(TimeZoneName.Eastern)) return TimeZoneName.Eastern;
        else return TimeZoneName.Unknown;

        bool TestOffset(TimeZoneName zone)
        {
            var info = GetZoneInfo(zone);
            var offset = info.IsDaylightSavingTime(date)
                ? info.BaseUtcOffset.Add(TimeSpan.FromHours(1))
                : info.BaseUtcOffset;
            return Equals(date.Offset, offset);
        }

        TimeZoneInfo GetZoneInfo(TimeZoneName zone)
        {
            switch (zone)
            {
                case TimeZoneName.Hawaiian: return TimeZoneInfo.FindSystemTimeZoneById("Hawaiian Standard Time");
                case TimeZoneName.Alaskan: return TimeZoneInfo.FindSystemTimeZoneById("Alaskan Standard Time");
                case TimeZoneName.Pacific: return TimeZoneInfo.FindSystemTimeZoneById("Pacific Standard Time");
                case TimeZoneName.Mountain: return TimeZoneInfo.FindSystemTimeZoneById("Mountain Standard Time");
                case TimeZoneName.Central: return TimeZoneInfo.FindSystemTimeZoneById("Central Standard Time");
                case TimeZoneName.Eastern: return TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time");
                case TimeZoneName.Unknown: throw new NotSupportedException("TimeZone.Unknown");
                default: throw new TimeZoneNotFoundException();
            }
        }
    }
}