Format Days To Hours

In the past, I have used a formula to calculate how many work days has 
occurred between date fields.  I track days excluding Holidays and
Weekends 
from code I received years back from this discussion group.  Everything
works 
wonderful.

I have another situation similiar but the user wants to track time as well

as the number of days excluding Holidays and Weekends.  Is there a way to 
format this formula
CalcWorkDays([DateTimeReceived],[DateTimeAcknowledged]) 
so I can get hh:mm:ss?  Currently I am get 1 day. Is there a way to format
1 
day to 15 minutes or should I use another public function? 

For instance:
DateTimeReceived                      DateTimeAcknowledged
4/4/08 10:00 am                        4/4/08  10:15 am

Here is the code:
Function CalcWorkDays(dtmStart As Date, dtmEnd As Date) As Integer
Dim intTotalDays As Integer ' Counter for number of days
Dim dtmToday As Date        ' To increment the date to compare
'Compliments of Dave Hargis

    intTotalDays = DateDiff("d", dtmStart, dtmEnd) + 1  'Start with total
days
                                                        'Add one to
include 
First Day
    dtmToday = dtmStart                                 'Initiate compare
date
    Do Until dtmToday > dtmEnd
        If Weekday(dtmToday, vbMonday) > 5 Then         'It is Saturday or

Sunday
            intTotalDays = intTotalDays - 1             'Take one day away
        ElseIf Not IsNull(DLookup("[Holdate]", "Holidays", _
                "[Holdate] = #" & dtmToday & "#")) Then 'It is a holiday
            intTotalDays = intTotalDays - 1             'Take one day away

for the Holiday
        End If
    dtmToday = DateAdd("d", 1, dtmToday)                'Add a day for
next 
compare
    Loop    'Until dtmToday > dtmEnd                    'All days have
been 
compared
    CalcWorkDays = intTotalDays                         'Return the value
        
End Function