If all of the tables are laid out as per the original definition then it would just be a matter of looping through each table:
Sub ScratchMacro()
'A basic Word macro coded by Greg Maxey, http://gregmaxey.com/word_tips.html, 1/2/2019
Dim oTbl As Word.Table
Dim lngIndex As Long, lngTbl as Long
Dim var1, var2, var3
For lngTbl = 1 to ActiveDocument.Tables.Count
Set oTbl = ActiveDocument.Tables(lngTbl)
For lngIndex = 2 To oTbl.Rows.Count
var1 = fcnCellText(oTbl.Rows(lngIndex).Cells(2)): var2 = fcnCellText(oTbl.Rows(lngIndex).Cells(3))
If IsDate(var1) And IsDate(var2) Then
var3 = DateDiff("n", var1, var2)
Select Case var3
Case Is >= 2: oTbl.Rows(lngIndex).Cells(4).Range.Text = var3 & " min. wait"
Case Else
oTbl.Rows(lngIndex).Cells(4).Range.Text = ""
End Select
End If
Next lngIndex
Next lngTbl
lbl_Exit:
Exit Sub
End Sub