using System;

using System.Globalization;

public class Program

{

    public static void Main()

    {

        String timeFromServer = "2019-02-07T06:32:56.457Z";

        String timeZoneFromServer = "-03:00";

        DateTime dateValue = DateTime.ParseExact(timeFromServer, "yyyy-MM-ddTHH:mm:ss.fffZ", CultureInfo.InvariantCulture);

​

        bool isNegative = timeZoneFromServer.StartsWith("-");

        string format = isNegative ? "\\-hh\\:mm" : "\\+hh\\:mm";

        TimeSpanStyles tss = isNegative ? TimeSpanStyles.AssumeNegative : TimeSpanStyles.None;

        TimeSpan ts;

         if (TimeSpan.TryParseExact(timeZoneFromServer, format, null, tss, out ts))

        {

            Console.WriteLine("{0} successfully parsed to: {1}", timeZoneFromServer, ts);

            String stringFromTimeSpan = ts.ToString(@"hh\:mm");

            Console.WriteLine("stringFromTimeSpan = " + stringFromTimeSpan);

        }

        else

        {

            Console.WriteLine("Could not be parsed: {0}", timeZoneFromServer);

            dateValue = DateTime.Now;

        }

        dateValue = dateValue + ts;

    }

}