In honor of Patriot Day, Sept. 11, the United States flag is to be lowered from sunrise through sunset on Sunday, Sept. 11. For state government buildings and other entities that are closed on weekends, it is permissible to lower the flag at 5 p.m. the preceding Friday and raise it the following Monday morning.
The full text of the presidential proclamation can be found here: A Proclamation on Patriot Day and National Day of Service and Remembrance.