In keeping with tradition, Apple has shared the App Store Connect's holiday program, useful for developers who need to plan new apps and updates during the holidays.
Apple has announced the 2019 holiday calendar in a publication on its website for developers:
The most intense season of the store is almost there. Make sure your apps are day and ready for the holidays. New apps and updates will not be accepted from December 23rd to December 27th (Pacific Time). Therefore, all versions must be planned, sent and approved in advance. Other features of the App Store Connect and the developer account will remain available.