A quick way per report, is to add the print date and time and the data date and time (from the field explorer->special fields). If you save the report exactly when it finishes executing, you can then calculate the difference. In certain cases, you need to make a quick change to something in the report, e.g., stretch the size of a field, and then save to get the print time to update (which should reflect the currentdatetime).
-LB