Calculate Working Hours

I am creating a database and what I need is code to figure out working hours between a start date and end date minus weekends & holidays.  I am not familiar with how to get this to work using queries etc.  I found code below but do not know how to have this run and fill a field in the table for the form named StaplesTotalTime.  The fields for start and end date/time are StaplesOutStart and StaplesOutEnd.  Thanks for any help.

Public Function NetWorkhours(dteStart As Date, dteEnd As Date) As Single
 
Dim intGrossDays As Integer
Dim intGrossHours As Single
Dim dteCurrDate As Date
Dim i As Integer
Dim WorkDayStart As Date
Dim WorkDayend As Date
Dim nonWorkDays As Integer
Dim StartDayhours As Single
Dim EndDayhours As Single
 
NetWorkhours = 0
nonWorkDays = 0
 
'Calculate work day hours on 1st and last day
WorkDayStart = DateValue(dteEnd) + TimeValue("09:00am")
WorkDayend = DateValue(dteStart) + TimeValue("05:30pm")
StartDayhours = DateDiff("h", dteStart, WorkDayend)
EndDayhours = DateDiff("h", WorkDayStart, dteEnd)
 
'adjust for time entries outside of business hours
If StartDayhours < 0 Then StartDayhours = 0
If EndDayhours > 8.5 Then EndDayhours = 8.5
 
'Calculate total hours and days between start and end times
intGrossDays = DateDiff("d", (dteStart), (dteEnd))
intGrossHours = DateDiff("h", (dteStart), (dteEnd))
 
'count number of weekend days and holidays (from a table called "Holidays" that lists them)
For i = 0 To intGrossDays
        dteCurrDate = dteStart + i
        If Weekday(dteCurrDate, vbSaturday) < 3 Then
            nonWorkDays = nonWorkDays + 1
        Else
            If Not IsNull(DLookup("[HolDate]", "Holidays", "[HolDate] = #" & Int(dteCurrDate) & "#")) Then
                nonWorkDays = nonWorkDays + 1
            End If
        End If
 Next i
    
'Calculate number of work hours
Select Case intGrossDays
 Case 0   'start and end time on same day
    NetWorkhours = intGrossHours
 Case 1   'start and end time on consecutive days
    NetWorkhours = NetWorkhours + StartDayhours
    NetWorkhours = NetWorkhours + EndDayhours
 Case Is > 1  'start and end time on non consecutive days
    NetWorkhours = NetWorkhours - (nonWorkDays * 24)
    NetWorkhours = (intGrossDays - 1 - nonWorkDays) * 8.5
    NetWorkhours = NetWorkhours + StartDayhours
    NetWorkhours = NetWorkhours + EndDayhours
 End Select
 
End Function

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