John,

I would think the date/time of the latest run should be stored in a
table somewhere.  You could make a simple table with one field and one
record, specifically for this purpose.  Then, add an action to the macro
itself to run an Update Query to change the value of this date/time to
Now().  And then, I suppose, bind the switchboard to this table, or add
this table to the query (if any) that the switchboard is currently bound
to, or put an unbound textbox on the switchboard form and use the
DLookup() function to retrieve the date/time value from the table.  Hope
that makes  sense.