How can you give advance notice to someone who has not been in your bank? If they are already customers then the new account exception will not work for a new account that a current or recent customer opens.
Reg CC considers an account as new for its first 30 days. So an account opened yesterday that received the old disclosure would be entitled to a change notice today, as they would be subject to the new terms.
Advance notice isn't required and technically notice is required within 30 days after the change. At that time the change doesn't apply. Reg CC does say "A bank shall send a notice to holders of consumer accounts at least 30 days before implementing a change to the bank's availability policy
regarding such accounts, except that a change that expedites the availability of funds may be disclosed not later than 30 days after implementation." Since those accounts won't be affected (they aren't "new" after the 30 days), I could make a case that no notice is required. I suppose technically the 30th day is the hangup, but since it is a favorable change, someone would really have to want to cite you/be on a witch hunt on something questionable like this. Be sure to change it on the disclosures given when you make the change so your practices match your policy.