search for dates in excel worksheet and add one hour - excel

Question

I have a sheet where all dates are in the wrong timezone. I need to add one hour to all cells formated as dates, but leave the rest intact.
I found this:
Public Function AddHour(ByVal sTime As String) As String
Dim dt As Date
dt = CDate(sTime)
dt = DateAdd("h", 1, dt)
AddHour = Format(dt, "mm/dd/yy h:nnam/pm")
End Function
Now, how do I find the cells with dates in them?
Sub AddHour(ByVal ThisSheet As Worksheet)...

Answer 1

The code below was modified to apply additional information you provided in your comment below.
Option Explicit
Public Sub AddHour()
' 17 Dec 2017
Const FirstColumn As String = "A" ' set as required
Const LastColumn As String = "AV" ' set as required
Dim Ws As Worksheet
Dim Cf As Long, Cl As Long ' first / last column
Dim Dt As Double
Dim Rl As Long ' last used row (in column C)
Dim R As Long, C As Long
Set Ws = Worksheets("AddHour") ' replace with your sheet's name
Application.ScreenUpdating = False
With Ws
Cf = Columns(FirstColumn).Column
Cl = Columns(LastColumn).Column
For C = Cf To Cl
Application.StatusBar = Cl - C + 1 & " columns remaining"
Rl = .Cells(.Rows.Count, C).End(xlUp).Row
For R = 1 To Rl ' start looking in row 1 (amend if necessary)
With .Cells(R, C)
If IsDate(.Value) Then
Dt = .Value
' add 1 hour if there is a Time value in the date
If Dt - Int(Dt) Then .Value = Dt + (1 / 24)
End If
End With
Next R
Stop
Next C
End With
With Application
.ScreenUpdating = True
.StatusBar = False
End With
End Sub
You still have to replace the worksheet name "AddHour" in the code with whatever name your worksheet really has and specify the first and last columns where your dates are. You can change the first row in which the code starts looking for them.
The code presumes that your dates are "true" dates. You can test this by selecting any cell with a date you want to change and set its cell format temporarily to "General". If the date is a "true" date a number will be displayed instead of the date, like 43086.5046489583. If the display in the cell doesn't change upon reformatting then your dates are "Text" and must be treated differently.

Answer 2

If you are absolutely certain, that all dates in your sheet have to be modified you could loop over all cells in your used range and make the adjustments using your function like so:
Sub ChangeDate()
Dim rngDates As Range
Dim varCounter As Variant
Dim dt As Date
Application.ScreenUpdating = False
Application.DisplayAlerts = False
Application.Calculation = xlManual
Set rngDates = ThisWorkbook.Worksheets("Tabelle2").UsedRange
'Loop over all cells in range
For Each varCounter In rngDates
'If it's a date, change its value
If IsDate(varCounter.Value) Then
dt = CDate(varCounter.Value)
dt = DateAdd("h", 1, dt)
varCounter.Value = Format(dt, "mm/dd/yy h:nnam/pm")
End If
Next varCounter
Application.ScreenUpdating = True
Application.DisplayAlerts = True
Application.Calculation = xlAutomatic
End Sub
Depending on the amount of cells in your used range this might not be very performant.
To improve on that we can read your used range into an array and process it in memory like so:
Sub ChangeDate()
Dim varValues As Variant
Dim lngColumns As Long, lngRows As Long
Dim dt As Date
Application.ScreenUpdating = False
Application.DisplayAlerts = False
Application.Calculation = xlManual
'Read entire range to array
varValues = ThisWorkbook.Worksheets("Tabelle2").UsedRange
'Loop over all "columns"
For lngColumns = 1 To UBound(varValues, 1)
'Loop over all "rows" in that "column"
For lngRows = 1 To UBound(varValues, 2)
If IsDate(varValues(lngColumns, lngRows)) Then
dt = CDate(varValues(lngColumns, lngRows))
dt = DateAdd("h", 1, dt)
varValues(lngColumns, lngRows) = Format(dt, "mm/dd/yy h:nnam/pm")
End If
Next lngRows
Next lngColumns
'Overwrite usedRange with array
ThisWorkbook.Worksheets("Tabelle2").UsedRange = varValues
Application.ScreenUpdating = True
Application.DisplayAlerts = True
Application.Calculation = xlAutomatic
End Sub
This should be quiet performant regardless of the amount of data you're processing.
It goes without saying that this might not account for everything without having seen your workbook and has to be thoroughly tested.