Voor een applicatie moest herhaaldelijk uitgerekend worden hoeveel dagen er in een bepaalde periode zitten.
De volgende functie voldeed hier goed:

Input: getDaysBetween("31-12-2007","01-01-2007", "1,7" ,"25/12/07 - 26/12/07,05-12-2007",Doc)  

Output: 258

Private Function getDaysBetween(strStart As String, strEnd As String,daysToExclude As String , datesToExclude As String ,Doc As NotesDocument) As Long
 On Error Goto ErrorHandler
 Dim Formula As Variant
 Dim dLow As String
 Dim dHigh As String
 
 If strStart = "" Or strEnd = "" Then Goto ErrorHandler
 
 strStart = {@TextToTime("} & strStart & {")}
 strEnd= {@TextToTime("} & strEnd & {")}
 
 If daysToExclude = "" Then
  dLow = {;0}
 Else
  dLow = {;@TextToNumber(@Explode("} & daysToExclude & {";","))}
 End If
 
 If Not datesToExclude = "" Then
  dLow = dLow & {;@TextToTime(@Explode(@TextToTime(@Explode("} & datesToExclude & {";","))))}
 End If
 
 dHigh$ = {@BusinessDays(} & strStart$ & {;} & strEnd$ & dLow & {)}
 dLow$ = {-@BusinessDays(} & strEnd$ & {;} & strStart$ & dLow & {)} 
 
 Formula = Evaluate({@If(} & strStart & {>} & strEnd & {;} & dLow$ & {;} & dHigh$ & {)} ,Doc)
 
 getDaysBetween = Clng(Formula(0))
 
 Exit Function
ErrorHandler:
  Print Lsi_info(2) & " : Error " & Error & " (" & Err & ") on line " & Erl & "."
  getDaysBetween = 0
  Exit Function
  Resume Next
End Function