Some would be ready to teach at 100 dives while many, many others are unfit to teach even after thousands of dives. Many instructors just don't have the sense God gave a goose and they certainly pose a risk to their students largely due to their hubris. If you "don't get it", I'm afraid that even 30 months of training may fail to make you a competent instructor. If you do "get it", then 30 days might be sufficient. It depends on the person and their motivation for excellence.