From my experience, it would be better to wait until the the beer is kegged/bottled. The coffee aroma fades rather fast.
I did an Imperial Coffee Porter a few years ago. For that beer, I dry-beaned the beer with 2oz of course ground coffee for 2 days and then added 2 double shots of espresso at kegging. When fresh, the beer was an incredible coffee flavor, aroma bomb. After a few months, the coffee had faded to more of a chocolate flavor with no aroma.