VBA local timezone adjustment - vba

Question

Say I have a local Pacific Time (UTC-8) Excel value. For example 41656.67297 is 17 January 2014 4:09 PM. I do not have control of this value.
I want to adjust the given value relative to the users local time. Say for example someone in Dublin is using the Excel workbook. I want to adjust the given number and display it in his local time, 18 January 2014 12:09 AM. Is there any built in Excel functionality to make this smooth?

Answer 1

VBA doesn't provide an option for this natively, but there's a Windows API that will allow you to do what you're looking for. This article describes how to do so and here is the MSDN page on GetTimeZoneInformation.
From the CPearson page, make these declarations first:
Option Explicit
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
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' NOTE: If you are using the Windows WinAPI Viewer Add-In to get
' function declarations, not that there is an error in the
' TIME_ZONE_INFORMATION structure. It defines StandardName and
' DaylightName As 32. This is fine if you have an Option Base
' directive to set the lower bound of arrays to 1. However, if
' your Option Base directive is set to 0 or you have no
' Option Base diretive, the code won't work. Instead,
' change the (32) to (0 To 31).
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
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)
Then this function will find the user's local time and offset from GMT:
Function LocalOffsetFromGMT(Optional AsHours As Boolean = False, _
Optional AdjustForDST As Boolean = False) As Double
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' 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.)
' Note that the return type of the function is a Double not a Long. This
' is to accomodate those few places in the world where the GMT offset
' is not an even hour, such as Newfoundland, Canada, where the offset is
' on a half-hour displacement.
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
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
You can test the code with:
MsgBox (LocalOffsetFromGMT())
Then to add this offset to the original time you can do the following:
OriginalTime + TIME(LocalOffsetFromGMT(True, True), 0, 0)