If we want to change our deposit cut-off time to an hour later (which actually benefits our customers), do we need to give a 30 day prior notice to the change?

No, but you do need to give it by 30 days after the change, since it does expedite the availability of funds:

See Reg CC 229.18(e)Changes in policy. 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.