Personally, I'd be inclined to bookmark the table or bind it to a suitably-titled rich text content control, so it no longer matters where the table occurs in the document. Then you could use code like:
Code:
Dim Rng As Range, i As Long
With ActiveDocument.Bookmarks("MyTable").Range.Tables(1)
Set Rng = .Cell(Row:=3, Column:=3).Range
i = Len(Rng.Text) - 1
If i > 40 Then
MsgBox "40 Char Description: Exceeded Character Limit of 40 " & "(" & i & ")"
End If
End With
The code for a table bound to a content control is similar.