VBA Function Vs cells operations

[korrrro]

Hi,

I`ve got a problem with cells format operations under the Function.
There is the code below and after IF I`d like to clear content of active cell and the cell above or change their color to another but it doesn`t work (but for example merging cells works). The question is why ? It works under Sub but not under Function.
Thanks for help in advance

Option Explicit 

Function Odliczanie2(data1a As String) As String 

Dim data2 As Date 
Dim data1 As Date 
Dim data2godzina As Integer 
Dim data2dzien As Integer 
Dim roznicaSekundy As Long 

data2 = Now() 

If IsDate(data1a) Then 
  data1 = CDate(data1a) 
  roznicaSekundy = DateDiff("s", data2, data1) 
  data2dzien = Int(roznicaSekundy / 86400) 
  data2godzina = Round((roznicaSekundy - (data2dzien * 86400)) / 3600) 
  
  If roznicaSekundy < 0 Then 
    Odliczanie2 = "PO CZASIE !" 
  Else 
    Odliczanie2 = data2dzien & " d " & data2godzina & " godz " 
  End If 
Else 
  Range(ActiveCell, ActiveCell.Offset(-1, 0)).Clear 
                                                             'lub .Interior.ColorIndex = 23 
End If 


End Function

Excell file attached.
For example column "2" cells F12 and F13.

[korrrro]

And example attached

[westconn1]

how are you calling the function?

[korrrro]

It`s in the file attached. "=Przykład.xls!Odliczanie2.Odliczanie2(E12)"

[westconn1]

changing values to other cells is not possible when called as a worksheet function
as a function it will work if called from someother procedure, but not from a formula

only suggestion i can think of to try is to use application.ontime to call another procedure after a small delay, so that the function can finish first, before clearing the cell