You have to reach maximum medical benefit is the wording I believe. It is difficult for the many conditions to reach that state in less than a year. Many conditions don't reach that for many many years. However, there is an assumption that after 12 months they are close enough. The MTF commander has to approve a profile extension further than that.
Each branch has their own profiling regs. AR 40-501 chapter 7 has the majority of the relevant stuff for the Army.
Profiling doesn't really have a reputation of being about medicine. Its more about administrative paperwork, so most docs don't really understand it well and just wing it. Reading a regulation isn't important to many docs. I feel it would be a likely estimate that 50% of profiles have a couple things wrong with them. It is not uncommon to find a specialist unwilling to even touch them.
What is the treatment being offered and what is the likelihood of success? The answers to that is really the important thing for determining if a permanent profile should be issued in less than 12 months. If there is treatment to explore, a permanent profile isn't appropriate IMO.