Help with Time Condition/Time Group

I’m hoping someone can give me a quick pointer on a Time Condition/Time Group setup. The system is currently set up with one Time Group for the “open hours” 8:30-4:30 Mon-Fri… it is used by one Time Condition to send the calls to a ring group during “open hours” and to the “closed IVR” otherwise.

The customer is going to be closed over Christmas from 4:30pm on Dec 20th and re-open at 8:30am on Jan 6th so they will want all of the calls to go to the “closed IVR” during the whole time period.

I’m not quite sure the best way to add this holiday into the existing logic.