Refer to §229.18(e). Any time there is a change in an institution’s availability policy, a notice must be sent to affected consumers. If the change is adverse to the customer (the amount delayed is more or the availability times are longer), the notice must be provided 30 days before implementing the change. If the change is beneficial to the customer (the amount delayed is less or the availability times are sooner), the notice must be provided no later than 30 days after implementing the change.
Notice this only has to be sent to consumers although Reg CC applies to business customers as well. Since the change is in the consumer's favor, you don't have to tell them 30 days prior, but you do have to tell them no later than July 30th. You need to let them know, as applicable, that the amount that you can delay for personal checks is changing from $200 to $225 and exception holds is changing from $5,000 to 5,525. Something like this:
Effective 7/1/2020, we are increasing the amount we make available for withdrawal by checks not subject to next day availability to $225. In addition, the amount available for withdrawal on exception holds for large deposits, new accounts and the amount for determining a repeat overdraft is increasing to $5,525.