Wouldn't include it in the letter - sounds structured and not genuine IMO
But keep track of that yourself bc need to enter in AACOMAS
I think I did about 60 hours in total (urology, maxillofacial surg, neurologist), but I agree with Goro, the more the better, however, if you take experiences from X hours and are able to articulate that in your app/PS/essays, you did your job.