I did test and modify code in your db. And that last one looked really good but testing for all possible permutations can be more art than science. This time I manually calculated the expected results for the given sample. Then I started over from scratch with the original code. This version returns the same values as my manual calcs.


Code:
Public Function NetWorkMinutes(rdteStart As Date, rdteEnd As Date) As Long
    Dim lngFirstDayMins As Long
    Dim lngLastDayMins As Long
    Dim dteWork As Date
    Dim dteStart As Date
    Dim dteEnd As Date
    Dim intMinutes As Integer
    Dim dblStartTime As Double
    Dim dblEndTime As Double
    
    'Supplied end date-time earlier or equal start date-time, so exit.
    If rdteEnd <= rdteStart Then NetWorkMinutes = 0: GoTo Exit_Procedure
    
    'If the start date is a Sunday or holiday then reset it to following day.
    Do
        Select Case DatePart("w", rdteStart, vbMonday)
            Case 7  'Sunday
                rdteStart = DateAdd("d", 1, Int(rdteStart)) + TimeValue("06:30:00")
            Case Else
                If IsHoliday(rdteStart) Then
                    Select Case DatePart("w", rdteStart, vbMonday)
                        Case 1
                            rdteStart = Int(rdteStart) + TimeValue("6:30:00") + 1
                        Case Else
                            rdteStart = Int(rdteStart) + TimeValue("10:00:00") + 1
                    End Select
                Else
                    Exit Do     'Not Sunday or holiday.
                End If
        End Select
    Loop
    
    'If the end date is a Sunday then reset it to previous day.
    Do
        Select Case DatePart("w", rdteEnd, vbMonday)
            Case 7  'Sunday
                rdteEnd = DateAdd("d", -1, Int(rdteEnd)) + TimeValue("13:30:00")
            Case Else
                If IsHoliday(rdteEnd) Then
                    If DatePart("w", rdteEnd, vbMonday) = 1 Then
                        rdteEnd = DateAdd("d", -2, Int(rdteEnd)) + TimeValue("13:30:00")
                    Else
                        rdteEnd = DateAdd("d", -1, Int(rdteEnd)) + TimeValue("22:00:00")
                    End If
                Else
                    Exit Do     'Not Sunday or holiday.
                End If
        End Select
    Loop
    If rdteEnd > rdteStart Then
        Select Case DatePart("w", rdteStart, vbMonday)
            Case 6
                dblEndTime = TimeValue("13:30:00")
            Case Else
                dblEndTime = TimeValue("22:00:00")
        End Select
        Select Case DatePart("w", rdteEnd, vbMonday)
            Case 6
                dblStartTime = TimeValue("10:00:00")
            Case Else
                dblStartTime = TimeValue("06:30:00")
        End Select
        
        'Special case if adjusted date start equals adjusted date end.
        'Else calculate first and last day minutes.
        If Int(rdteStart) = Int(rdteEnd) Then
            NetWorkMinutes = DateDiff("n", rdteStart, rdteEnd)
            GoTo Exit_Procedure
        Else
            lngFirstDayMins = DateDiff("n", rdteStart - Int(rdteStart), dblEndTime)
            lngLastDayMins = DateDiff("n", dblStartTime, rdteEnd - Int(rdteEnd))
        End If
        
        'Set the start and end dates for full work days (i.e. exclude first
        'and last days) and iterate through period testing for holidays and weekends.
        
        dteWork = Int(DateAdd("d", 1, rdteStart))
        dteEnd = Int(DateAdd("d", -1, rdteEnd))
        intMinutes = 0
        Do Until Int(dteWork) = Int(rdteEnd)
            If Not IsHoliday(dteWork) Then
                Select Case DatePart("w", dteWork, vbMonday)
                Case 6
                    dteStart = dteWork + TimeValue("10:00:00")
                    dteEnd = dteWork + TimeValue("13:30:00")
                Case Else
                    dteStart = dteWork + TimeValue("6:30:00")
                    dteEnd = dteWork + TimeValue("22:00:00")
                End Select
            End If
            intMinutes = intMinutes + DateDiff("n", dteStart, dteEnd)
            dteWork = DateAdd("d", 1, dteWork)
        Loop
        NetWorkMinutes = intMinutes + lngFirstDayMins + lngLastDayMins
    End If
    
Exit_Procedure:
    Exit Function
End Function
I did only one test with a holiday in the middle of range by specifying a holiday date (10/14) in the IsHoliday function.