My understanding is: you want to be a delayed availability bank for the first twelve months after the account is opened. Then, you would normally expect to become a next day availability bank. When Reg CC first took effect it had a two-year phase in period; i.e. many banks disclosed their hold policy and, in the same disclosure, indicated it would change on September 1, 1990 and spelled out what the successor policy would be. As long as you have an "old" examiner, there should not be any question about your ability to liberalize your policy based on the passage of time.
Your disclosure could use model language in most respects, but the first (delayed availability) portion might be prefaced with, "For the first twelve months after your account is open…" The second (next day availability section) could begin, "After your account has been open for twelve months…" You might bold face the prefatory language and put light borders around the paragraphs to segregate the first and then the second time periods.
Retaining the right to extend your status as a delayed availability bank is the drafting challenge. For the sake of discussion, at the end of the first section (delayed availability) you could add: "If in the first twelve months your account is open there are difficulties in its handling, for example, high volumes of returned checks, either deposited into or written on the account, we reserve the right to extend this delayed availability policy for an additional year. If we decide to take this step, you will receive written notification." This is not significantly different than your language, aside from the fact that I would not expect the customer to understand the reference to "Regulation CC."
You should avoid references to "new account" or "new customer" in your dislcosure. Those phrases will have engrained meanings to many reviewers. References to case by case holds would be in the second section. Exception holds would be referenced after the second section.
As you note, routinely delaying availability for two and five days on local and nonlocal checks is your bank's prerogative, regardless of your reason. However, the comments above might be a fair indicator of the initial confusion this approach will generate among those attempting to analyze it; it might be prudent to keep a file memorandum explaining your rationale. (You might not be there to explain it when the day comes.) In any case, it's going to be one long disclosure.