Officials have extended the hours of the National Museum of African American History and Culture so more visitors may experience. (Photo by Jahi Chikwendiu/The Washington Post)

Due to high demand, Smithsonian officials will extend the hours of the National Museum of African American History and Culture, making available some 80,000 additional passes from the Sept. 24 opening through Oct. 2.

The new timed passes will be available on Sept. 6 at 9 a.m. on the museum website at nmaahc.si.edu or by calling 800-514-3849 or 919-653-0443 between 9 a.m. and 8 p.m. Monday through Saturday and noon to 8 p.m. Sunday. There is a limit of 6 timed passes per order.

Hours on the opening day, Sept. 25, have been extended two hours until 8 p.m. (because a reception is scheduled to begin at 9 p.m.) On Sunday, Sept. 25, the museum will open at 7 a.m. – three hours earlier – and remain open until midnight.

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The next five days – from Sept. 26 through Sept. 30 – the museum will open from 10 a.m. to 7:30 p.m., adding an additional 2 hours. Hours for Saturday, Oct. 1 are 10 a.m. to midnight; on Sunday Oct. 2, it will be open from 10 a.m. to 10 p.m.

The museum will use timed passes through December, officials said.

The timed passes designate a 15-minute window for visitors to enter the museum. They are being used to control crowds and limit wait times at the museum's entrance. Once they have entered, visitors may spend as much time as they'd like in the museum.

The first free timed passes were snapped up when they became available Aug. 27.  All passes to the opening weekend were gone within an hour; by the end of the weekend, the only passes available were some mid-week days in October.

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Museum founding director Lonnie Bunch said he was humbled by the response from the public.

"As a result of this unprecedented interest, we are making more passes available so that as many people as possible can experience the museum in person during this historic moment and for years to come," Bunch said in a statement.

President Obama is expected to attend the Sept. 24 opening ceremony, which begins with an hour of music starting at 9 a.m., with the dedication beginning at 10 a.m. The museum will open to visitors at 1 p.m.