Get Timezone Information in VBA (Excel)

Question

I would like to determine a time offset to GMT/UTC (including daylight saving time) for different countries at a specific date in VBA. Any ideas?

EDIT (from self-an

Answer 1

Here is the code that is referenced in the answer by 0xA3. I had to change the declare statements to allow it run properly in Office 64bit but I haven't been able to test again in Office 32bit. For my use I was trying to create ISO 8601 dates with timezone information. So i used this function for that.

Public Function ConvertToIsoTime(myDate As Date, includeTimezone As Boolean) As String

    If Not includeTimezone Then
        ConvertToIsoTime = Format(myDate, "yyyy-mm-ddThh:mm:ss")
    Else
        Dim minOffsetLong As Long
        Dim hourOffset As Integer
        Dim minOffset As Integer
        Dim formatStr As String
        Dim hourOffsetStr As String

        minOffsetLong = LocalOffsetFromGMT(False, True) * -1
        hourOffset = minOffsetLong \ 60
        minOffset = minOffsetLong Mod 60

        If hourOffset >= 0 Then
            hourOffsetStr = "+" + CStr(Format(hourOffset, "00"))
        Else
            hourOffsetStr = CStr(Format(hourOffset, "00"))
        End If

        formatStr = "yyyy-mm-ddThh:mm:ss" + hourOffsetStr + ":" + CStr(Format(minOffset, "00"))
        ConvertToIsoTime = Format(myDate, formatStr)


    End If

End Function

The code below came from http://www.cpearson.com/excel/TimeZoneAndDaylightTime.aspx

Option Explicit
Option Compare Text
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
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' modTimeZones
' By Chip Pearson, chip@cpearson.com, www.cpearson.com
' Date: 2-April-2008
' Page Specific URL: www.cpearson.com/Excel/TimeZoneAndDaylightTime.aspx
'
' This module contains functions related to time zones and GMT times.
'   Terms:
'   -------------------------
'   GMT = Greenwich Mean Time. Many applications use the term
'       UTC (Universal Coordinated Time). GMT and UTC are
'       interchangable in meaning,
'   Local Time = The local "wall clock" time of day, that time that
'       you would set a clock to.
'   DST = Daylight Savings Time

'   Functions In This Module:
'   -------------------------
'       ConvertLocalToGMT
'           Converts a local time to GMT. Optionally adjusts for DST.
'       DaylightTime
'           Returns a value indicating (1) DST is in effect, (2) DST is
'           not in effect, or (3) Windows cannot determine whether DST is
'           in effect.
'       GetLocalTimeFromGMT
'           Converts a GMT Time to a Local Time, optionally adjusting for DST.
'       LocalOffsetFromGMT
'           Returns the number of hours or minutes between the local time and GMT,
'           optionally adjusting for DST.
'       SystemTimeToVBTime
'           Converts a SYSTEMTIME structure to a valid VB/VBA date.
'       LocalOffsetFromGMT
'           Returns the number of minutes or hours that are to be added to
'           the local time to get GMT. Optionally adjusts for DST.
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
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'''''''''''''''''''''''''''''''''''''''''''''''''''''
' Required Types
'''''''''''''''''''''''''''''''''''''''''''''''''''''
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

Public Enum TIME_ZONE
    TIME_ZONE_ID_INVALID = 0
    TIME_ZONE_STANDARD = 1
    TIME_ZONE_DAYLIGHT = 2
End Enum

'''''''''''''''''''''''''''''''''''''''''''''''''''''
' Required Windows API Declares
'''''''''''''''''''''''''''''''''''''''''''''''''''''
#If VBA7 Then
    Private Declare PtrSafe Function GetTimeZoneInformation Lib "kernel32" _
    (lpTimeZoneInformation As TIME_ZONE_INFORMATION) As Long
#Else
    Private Declare Function GetTimeZoneInformation Lib "kernel32" _
    (lpTimeZoneInformation As TIME_ZONE_INFORMATION) As Long
#End If

#If VBA7 Then
    Private Declare PtrSafe Sub GetSystemTime Lib "kernel32" _
        (lpSystemTime As SYSTEMTIME)
#Else
    Private Declare Sub GetSystemTime Lib "kernel32" _
        (lpSystemTime As SYSTEMTIME)
#End If




Function ConvertLocalToGMT(Optional LocalTime As Date, _
    Optional AdjustForDST As Boolean = False) As Date
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' ConvertLocalToGMT
' This converts a local time to GMT. If LocalTime is present, that local
' time is converted to GMT. If LocalTime is omitted, the current time is
' converted from local to GMT. If AdjustForDST is Fasle, no adjustments
' are made to accomodate DST. If AdjustForDST is True, and DST is
' in effect, the time is adjusted for DST by adding
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
Dim T As Date
Dim TZI As TIME_ZONE_INFORMATION
Dim DST As TIME_ZONE
Dim GMT As Date

If LocalTime <= 0 Then
    T = Now
Else
    T = LocalTime
End If
DST = GetTimeZoneInformation(TZI)
If AdjustForDST = True Then
    GMT = T + TimeSerial(0, TZI.Bias, 0) + _
            IIf(DST = TIME_ZONE_DAYLIGHT, TimeSerial(0, TZI.DaylightBias, 0), 0)
Else
    GMT = T + TimeSerial(0, TZI.Bias, 0)
End If
ConvertLocalToGMT = GMT

End Function


Function GetLocalTimeFromGMT(Optional StartTime As Date) As Date
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' GetLocalTimeFromGMT
' This returns the Local Time from a GMT time. If StartDate is present and
' greater than 0, it is assumed to be the GMT from which we will calculate
' Local Time. If StartTime is 0 or omitted, it is assumed to be the GMT
' local time.
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
Dim GMT As Date
Dim TZI As TIME_ZONE_INFORMATION
Dim DST As TIME_ZONE
Dim LocalTime As Date

If StartTime <= 0 Then
    GMT = Now
Else
    GMT = StartTime
End If
DST = GetTimeZoneInformation(TZI)
LocalTime = GMT - TimeSerial(0, TZI.Bias, 0) + _
        IIf(DST = TIME_ZONE_DAYLIGHT, TimeSerial(1, 0, 0), 0)
GetLocalTimeFromGMT = LocalTime

End Function

Function SystemTimeToVBTime(SysTime As SYSTEMTIME) As Date
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' SystemTimeToVBTime
' This converts a SYSTEMTIME structure to a VB/VBA date value.
' It assumes SysTime is valid -- no error checking is done.
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
With SysTime
    SystemTimeToVBTime = DateSerial(.wYear, .wMonth, .wDay) + _
            TimeSerial(.wHour, .wMinute, .wSecond)
End With

End Function

Function LocalOffsetFromGMT(Optional AsHours As Boolean = False, _
    Optional AdjustForDST As Boolean = False) As Long
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' LocalOffsetFromGMT
' This returns the amount of time in minutes (if AsHours is omitted or
' false) or hours (if AsHours is True) that should be added to the
' local time to get GMT. If AdjustForDST is missing or false,
' the unmodified difference is returned. (e.g., Kansas City to London
' is 6 hours normally, 5 hours during DST. If AdjustForDST is False,
' the resultif 6 hours. If AdjustForDST is True, the result is 5 hours
' if DST is in effect.)
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Dim TBias As Long
Dim TZI As TIME_ZONE_INFORMATION
Dim DST As TIME_ZONE
DST = GetTimeZoneInformation(TZI)

If DST = TIME_ZONE_DAYLIGHT Then
    If AdjustForDST = True Then
        TBias = TZI.Bias + TZI.DaylightBias
    Else
        TBias = TZI.Bias
    End If
Else
    TBias = TZI.Bias
End If
If AsHours = True Then
    TBias = TBias / 60
End If

LocalOffsetFromGMT = TBias

End Function

Function DaylightTime() As TIME_ZONE
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' DaylightTime
' Returns a value indicating whether the current date is
' in Daylight Time, Standard Time, or that Windows cannot
' deterimine the time status. The result is a member or
' the TIME_ZONE enum.
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
Dim TZI As TIME_ZONE_INFORMATION
Dim DST As TIME_ZONE
DST = GetTimeZoneInformation(TZI)
DaylightTime = DST
End Function