They are warm, they have food and rest rooms, and they are full of highlights of American history. And now, for the early birds to the National Mall, they will be open a bit longer on Inauguration Day because of an agreement between the Presidential Inaugural Committee and the Smithsonian Institution.

The National Museum of American History and the Castle, the first Smithsonian building and home to the Smithsonian Information Center, will open at 8 a.m. on Jan. 20, two hours earlier than usual. Linda St. Thomas, a Smithsonian spokeswoman, said the institution plans to increase its staffing to ensure that the buildings’ shops and cafes also open early and that bag checks proceed as swiftly as possible.

Ms. St. Thomas said that, while she did not know for certain, she believed this was the first time the Smithsonian had opened early on Inauguration Day.