I'm sure it is. Can you post a sample spreadsheet so we can better understand what you are trying to achieve?

I'd like to be able to put a start time for the meeting, and have the amount of time for each topic update the end time, and have the last end time roll up to the meeting end time.  Sound reasonable?
Agenda-Template.docx

You can insert a formula field in a table cell { = SUM(ABOVE) }.
Select the last cell in a column, choose Formula on the Layout tab and type
= SUM(ABOVE) into the dialogue.
Note that to update the total, press F9 when the field is in the selection.

Other field solutions that do not total columns can use bookmarked locations or Excel-like cell notation.

A VBA method with Content Controls would also be possible.

The agenda document may require some reformatting to make the template suitable for different types of agendas.  Times would have to be put in as minutes (as seems to be the current practice) or hours with fractions... (e.g. 1.5 hrs, 1.75 hrs) for the calculations you would not be able to mix minute format with hour format...

I'd suggest the approach implied by Grahams comment - the agenda items would need to be in a table and then sum up the table...  there would be quite a few calculations hidden in the document if you want to calculate the running time.  

Also if you were distributing to others PDF might be worth considering... (don't want people breaking the word document).

I think you can do this but it might be fiddly to use if using field codes.  The other option as per Grahams suggestion is VBA - if you are able to go down that path I think you can cut out a lot of complexity and make the overall document easier to work with.

Hope this helps,

A major point that I missed.

Word fields do not have a Date/Time calculation method. This link shows the complexity of using fields to calculate a given number of days ahead:
http://www.gmayor.com/insert_a_date_other_than_today.htm

Time-only calculations might be a bit simpler, but I can't think of a way to separate a piece of text like 11:30 into 11 and 30. The example above uses CreateDate three times to get each part of the current date. It doesn't start from text, so could use an arbitrary date.

This means that you will have to use VBA. The following code expects a ContentControl in cells 2 and 3 of each row in the table, except for the first (header) and last (total) row.

Private Sub Document_ContentControlOnExit(ByVal ContentControl As ContentControl, Cancel As Boolean)
    Dim tbl As Table
    Dim r As Integer
    Dim rw As Row
    Dim strTime1 As String
    Dim strTime2 As String
    Dim dtTime1 As Date
    Dim dtTime2 As Date
    Dim dtTotal As Date
    Dim dtDuration As Date
    
    If ContentControl.Range.Tables.Count = 1 Then
        Set tbl = ContentControl.Range.Tables(1)
        For r = 2 To tbl.Rows.Count - 1
            Set rw = tbl.Rows(r)
            strTime1 = rw.Cells(2).Range.ContentControls(1).Range.Text
            strTime2 = rw.Cells(3).Range.ContentControls(1).Range.Text
            rw.Cells(4).Range.Text = ""
            If IsDate(strTime1) Then
                dtTime1 = CDate(strTime1)
                If IsDate(strTime2) Then
                    dtTime2 = CDate(strTime2)
                    dtDuration = dtTime2 - dtTime1
                    rw.Cells(4).Range.Text = Format(dtDuration, "HH:nn:ss")
                    dtTotal = dtTotal + dtDuration
                End If
            End If
        Next r
        If CDbl(dtTotal) = 0 Then
            tbl.Rows.Last.Cells(4).Range.Text = ""
        Else
            tbl.Rows.Last.Cells(4).Range.Text = Format(dtDuration, "HH:nn:ss")
        End If
    End If
End Sub

Select allOpen in new window

If have modified the table in your document down to four rows for demonstration purposes and added Content Controls and the macro above in the ThisDocument module.

Note that the file extension should be put back to .docm after you have downloaded it.
Agenda-Template.docx

Graham,

I am having problems downloading and opening the file, even after changing the file extension to docm.

Alternative approach....

Does your agenda have substantial formatting that would preclude from performing the whole thing in Excel rather than Word.

A cell in excel can be set fairly wide and deep to accommodate multiple lines of text and then the time calculations would be much simpler.

Duration doesn't have to be added in true time format if you don't wish, it can use literal numbers so 45 would be 45 minutes or 00:45 if viewed in time format.

The link for finish time would also then be a lot simpler.

Thanks
Rob H

Example attached.
Excel-agenda.xlsx