The following notice and directive was sent out by the White House:
Please be advised that the flags should be lowered to half-staff immediately tonight, Friday September 18, 2020, for the death of Supreme Court Associate Justice Ruth Bader Ginsburg. The flags will be at half-staff until the day of interment.
U.S. Flag Code States
7. Position and manner of display (m)
“The flag, when flown at half-staff, should be first hoisted to the peak for an instant and then lowered to the half-staff position. The flag should be again raised to the peak before it is lowered for the day. […] The flag shall be flown at half-staff 30 days from the death of the President or a former President; 10 days from the day of death of the Vice President, the Chief Justice or a retired Chief Justice of the United States, or the Speaker of the House of Representatives; from the day of death until interment of an Associate Justice of the Supreme Court, a Secretary of an executive or military department, a former Vice President, or the Governor of a State, territory, or possession; and on the day of death and the following day for a Member of Congress.”
President Trump’s official proclamation will be available here when released: Proclamation