In less than an hour, museum supporters snapped up all ­28,500 tickets to the opening weekend of the National Museum of African American History and Culture after they went on sale Saturday morning. By Sunday afternoon, the only passes available to the Smithsonian museum were for weekdays in October.

Those who were quick enough to reserve the free tickets signed up for the date and a 15-minute window of time when they will be able to enter the museum, which opens Sept. 24. Officials hope this system will cut down on long wait times expected in the musem’s early months. For those who didn’t nab tickets, the museum will give out same-day passes starting Monday, Sept. 26. They will be distributed first-come, first-served starting at 9:15 a.m. each day.

Given the high demand, spokeswoman Linda St. Thomas said the Smithsonian will discuss ways to expand access to the museum. It may consider extending the museum’s hours, which are listed as 10 a.m. to 5:30 p.m.

“We’re thrilled at this level of interest,” St. Thomas said Sunday. “We would like to make sure everyone who wants to come is able to come at some point.”

The remaining tickets can be obtained 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 six passes per request. Tickets for November and December are not yet available, but officials plan to continue the reserved pass program indefinitely.

On the museum’s opening day, there will be a grand opening ceremony beginning at 10 a.m. President Obama is expected to be there. Tickets are not required to attend the outdoor ceremony, but the museum expects the crowd to be large enough to require multiple screens in the surrounding area so everyone can view the festivities.

The museum officially opens at 2 p.m., followed by an invitation-only gala at the Kennedy Center. On Sunday, it will remain open from 10 a.m. to midnight.

Inside, visitors will find 12 exhibitions containing nearly 3,000 objects in an 85,000-square-foot space. From the fedora of Michael Jackson to the casket of Emmett Till, the artifacts tell the story of African American life, history and culture. More than 300 volunteers have been trained to seek out and support visitors who become distressed by the exhibits that focus on slavery and other painful chapters of U.S. history. There will also be nurses on call.

To make the museum possible, more than $273 million was contributed from private donors, including the foundations of Oprah Winfrey, Bill and Melinda Gates, Shonda Rhimes, BET founder Robert L. Johnson and Michael Jordan.

Although construction of the museum was completed in less than four years, the idea for a place to celebrate African American achievements dates back to the early 1900s. In 1988, civil rights leader Rep. John Lewis (D-Ga.) introduced a bill in Congress to establish the museum. It failed. With each new Congress, for 15 years, Lewis proposed his bill, until President George W. Bush signed it Dec. 16, 2003.

Nine years later, Obama helped break ground on the building. Next month, as he prepares to end his tenure as the country’s first black president, he will see the opening of the only national museum devoted to the African American story.

Peggy McGlone contributed to this report.