The group can use Freedom Plaza through Dec. 30 at 10 p.m.
The permit excludes dates previously reserved by other permit holders, according to the Park Service. Alternate locations have been offered for those dates.
The Park Service has been in touch with all groups and organizations that hold finalized permits or have permits pending.
Four months is the maximum amount of time for which officials issue permits. If the Freedom Plaza group's permit change is approved, the demonstrators could apply for a new permit after four months, Carol B. Johnson, a spokeswoman for the National Park Service, told the Associated Press.
At the demonstrators' camp on Pennsylvania Avenue, people were settling in, and some of the uneasiness of Monday -- when demonstrators thought they might be arrested for overstaying their permit -- was gone. More than two dozen tents were set up in the rectangular plaza, where a map of the city is marked on the ground in light and dark stones. Stations for legal advice, first aid and food were running, though kitchen supplies and tarps for expected rain were needed. A white board showed plans for the day.
"We're able to concentrate on the things we came here to accomplish," said Mike Sheffer, 54, of Brandon, Vt., who said he came to protest the influence of corporations on government.
On Tuesday, six of the protesters were arrested for demonstrating inside a U.S. Senate office building and attempting to unfurl a banner that said "Tax the Rich.''
The protesters marched Tuesday afternoon with another group of demonstrators, Occupy D.C., which has been organizing marches from nearby McPherson Square. The group in Freedom Plaza has been using the slogan October 2011/Stop the Machine. The demonstration was organized to coincide with last week's 10th anniversary of the start of the war in Afghanistan. Both groups have said they support each other, however, and more coordination between the groups has been happening.
Lee Statum, 52, a demonstrator from Alabama, said she has no plans to leave Freedom Plaza any time soon. She spent her last $150 on a train ticket to the capital in order to protest corporate influence, she said.
"I'm here 'til it's over," she said.