I do this with one of my costing Dbases (tracking last time the price was updated). I accomplished it by using a child table holding only the cost and last date modified. In your case it would be the Speak_with_Rep field and the last date modified.
With these two fields in a different table, you can set the autoenter timestamp (or date) properties to update when the record is modified. Since there are only these fields, the record is only modified when the Speak_with_Rep field is modifed.
There is probably a slicker way to accomplish your goal, but this one works too.