Old thread or not... You can't see the additional box delay on a distributor machine, because the box is not in the circuit. But you certainly can see it with a timing light. The light flashes when the spark actually happens, since it's triggered by the current passing down the plug wire... which will be a couple of degrees later (retarded) by the box.
We may not notice it except to observe a little less advance at higher RPM than expected. But it's definitely included in the circuit from reluctor tooth to plug ;)