Too many variables. 1 room or 2? How efficient is your nursing staff? Propofol or fent/versed? How good of an endoscopist are you? Are you taking off difficult polyps/doing EMR or sending all those out? Are you doing a lot of bogus EGDs for abdominal pain? What percentages are EGDs vs. colons?
6-14 cases in a half day is a reasonable estimate. If you are doing mostly colons and doing more than 8-9 though I would question the quality. Even if you are averaging 2-3 minute insertions and 7 minute withdrawals, there are always going to be difficult cases that throw off your timing. So if you estimating 15 minutes to do the actual colon, 5 minutes to write the report and talk to the next/last patient, and 5 minutes of turnover time, thats a case every 20-25 minutes. There are some groups that do it faster but who knows the quality.
Obviously you can do a normal EGD in like 2 minutes so if you stack a lot of those it can increase your numbers.