Assign the date for system.net email outlook appointment visual basic

I am using the following code to send an outlook appointment using system.net.mail The code works perfectly and i am able to receive the appointment. But the problem is i can't figure out how to assign the appointment start date or end date

    'Str.AppendLine(String.Format("DTSTART:{0:yyyyMMddTHHmmssZ}", DateTime.Now))
     Str.AppendLine(String.Format("DTSTAMP:{0:yyyyMMddTHHmmssZ}", DateTime.UtcNow))
     Str.AppendLine(String.Format("DTEND:{0:yyyyMMddTHHmmssZ}", DateTime.Now.AddHours(3)))

1) How do i set the UTC, as if i assign current date now it's always +8. can i just provide a date time without using UTC. 2) And how do i specify the date time in the code. cause right now it use DateTime.Now then works. But manual assign not working

The complete code as below

Dim testMessage As New System.Net.Mail.MailMessage
    Dim fromAddress As New System.Net.Mail.MailAddress("[email protected]")
    Dim objSmtpClient As New SmtpClient(smtpIP, 25)
    Dim mailAttachment As Attachment
    Dim iserror As Boolean = False




    Try

        testMessage.From = fromAddress
        testMessage.To.Add("[email protected]")
        testMessage.Subject = "Training Scheduled"
        testMessage.Priority = MailPriority.Normal
        testMessage.Body = "Test"
        testMessage.IsBodyHtml = False


        Dim Str As New System.Text.StringBuilder()
        Str.AppendLine("BEGIN:VCALENDAR")
        Str.AppendLine("PRODID:-//Schedule a Meeting")
        Str.AppendLine("VERSION:2.0")
        Str.AppendLine("METHOD:REQUEST")
        Str.AppendLine("BEGIN:VEVENT")
        Str.AppendLine(String.Format("DTSTART:{0:yyyyMMddTHHmmssZ}", DateTime.Now))
        'Str.AppendLine(String.Format("DTSTART:{0:yyyyMMddTHHmmssZ}", DateTime.Now))
        Str.AppendLine(String.Format("DTSTAMP:{0:yyyyMMddTHHmmssZ}", DateTime.UtcNow))
        Str.AppendLine(String.Format("DTEND:{0:yyyyMMddTHHmmssZ}", DateTime.Now.AddHours(3)))
        'Str.AppendLine(String.Format("DTEND:{0:yyyyMMddTHHmmssZ}", DateTime.Now))
        'Str.AppendLine("LOCATION: " + Me.Location)
        Str.AppendLine(String.Format("UID:{0}", Guid.NewGuid()))
        Str.AppendLine(String.Format("DESCRIPTION:{0}", testMessage.Body))
        Str.AppendLine(String.Format("X-ALT-DESC;FMTTYPE=text/html:{0}", testMessage.Body))
        Str.AppendLine(String.Format("SUMMARY:{0}", testMessage.Subject))
        Str.AppendLine(String.Format("ORGANIZER:MAILTO:{0}", testMessage.From.Address))

        Str.AppendLine(String.Format("ATTENDEE;CN=""{0}"";RSVP=TRUE:contact{1}", testMessage.[To](0).DisplayName, testMessage.[To](0).Address))

        Str.AppendLine("BEGIN:VALARM")
        Str.AppendLine("TRIGGER:-PT15M")
        Str.AppendLine("ACTION:DISPLAY")
        Str.AppendLine("DESCRIPTION:Reminder")
        Str.AppendLine("END:VALARM")
        Str.AppendLine("END:VEVENT")
        Str.AppendLine("END:VCALENDAR")

        Dim contype As New System.Net.Mime.ContentType("text/calendar")
        contype.Parameters.Add("method", "REQUEST")
        contype.Parameters.Add("name", "Meeting.ics")
        Dim avCal As AlternateView = AlternateView.CreateAlternateViewFromString(Str.ToString(), contype)
        testMessage.AlternateViews.Add(avCal)





        objSmtpClient.Send(testMessage)
    Catch ex As Exception
        'MessageBox.Show(ex.ToString)
        iserror = True
    Finally
        objSmtpClient = Nothing
        'alertMessage = Nothing
        fromAddress = Nothing
    End Try