The Daily Dose

Private Type SYSTEMTIME
    wYear As Integer
    wMonth As Integer
    wDayOfWeek As Integer
    wDay As Integer
    wHour As Integer
    wMinute As Integer
    wSecond As Integer
    wMilliseconds As Integer
End Type

Private Type TIME_ZONE_INFORMATION
    Bias As Long
    StandardName(0 To 31) As Integer
    StandardDate As SYSTEMTIME
    StandardBias As Long
    DaylightName(0 To 31) As Integer
    DaylightDate As SYSTEMTIME
    DaylightBias As Long
End Type

”””””””””””””””””””””””
‘ These give symbolic names to the time zone
‘ values returned by GetTimeZoneInformation .
”””””””””””””””””””””””

Private Enum TIME_ZONE
    TIME_ZONE_ID_INVALID = 0        ‘ Cannot determine DST
    TIME_ZONE_STANDARD = 1          ‘ Standard Time, not Daylight
    TIME_ZONE_DAYLIGHT = 2          ‘ Daylight Time, not Standard
End Enum

Private Declare Function GetTimeZoneInformation Lib "kernel32" _
    (lpTimeZoneInformation As TIME_ZONE_INFORMATION) As Long

Private Declare Sub GetSystemTime Lib "kernel32" _
    (lpSystemTime As SYSTEMTIME)

Public Function ConvertTimeToLocal(ByVal dtTime As Date, ByVal sZone As String) As Date
   
    Dim tzi As TIME_ZONE_INFORMATION
    Dim tz As TIME_ZONE
    Dim lGmtOff As Long
    Dim lBias As Long
   
    tz = GetTimeZoneInformation(tzi)
   
    lBias = tzi.Bias
    If tz = TIME_ZONE_DAYLIGHT Then lBias = lBias – 60
   
    Select Case UCase(sZone)
        Case "EDT"
            lGmtOff = -4
        Case "EST", "CDT"
            lGmtOff = -5
        Case "CST", "MDT"
            lGmtOff = -6
        Case "MST", "PDT"
            lGmtOff = -7
        Case "PST"
            lGmtOff = -8
        Case vbNullString
            lGmtOff = -tzi.Bias / 60
            If tz = TIME_ZONE_DAYLIGHT Then lGmtOff = lGmtOff + 1
    End Select
   
    ConvertTimeToLocal = dtTime + (TimeSerial(0, lBias, 0) + TimeSerial(lGmtOff, 0, 0))
   
End Function

Public Sub Test_ConvertTimeToLocal()
   
    Dim dtTestTime As Date
   
    dtTestTime = TimeSerial(9, 46, 13)
   
    Debug.Assert (ConvertTimeToLocal(dtTestTime, vbNullString) – dtTestTime) < TimeSerial(0, 0, 1)
    Debug.Assert (ConvertTimeToLocal(dtTestTime, "CDT") – dtTestTime) < TimeSerial(0, 0, 1)
    Debug.Assert (ConvertTimeToLocal(dtTestTime, "EST") – dtTestTime) < TimeSerial(0, 0, 1)
    Debug.Assert (ConvertTimeToLocal(dtTestTime, "EDT") – (dtTestTime + TimeSerial(1, 0, 0))) < TimeSerial(0, 0, 1)
    Debug.Assert (ConvertTimeToLocal(dtTestTime, "CST") – (dtTestTime – TimeSerial(1, 0, 0))) < TimeSerial(0, 0, 1)
    Debug.Assert (ConvertTimeToLocal(dtTestTime, "MDT") – (dtTestTime – TimeSerial(1, 0, 0))) < TimeSerial(0, 0, 1)
    Debug.Assert (ConvertTimeToLocal(dtTestTime, "MST") – (dtTestTime – TimeSerial(2, 0, 0))) < TimeSerial(0, 0, 1)
    Debug.Assert (ConvertTimeToLocal(dtTestTime, "PDT") – (dtTestTime – TimeSerial(2, 0, 0))) < TimeSerial(0, 0, 1)
    Debug.Assert (ConvertTimeToLocal(dtTestTime, "PST") – (dtTestTime – TimeSerial(3, 0, 0))) < TimeSerial(0, 0, 1)

End Sub