Armstrong had initially been set a February 6 deadline by USADA to answer questions under oath, but that was extended on Wednesday after the athlete's attorney Timothy Herman said the timing for an interview could not be accommodated.
"We have been in communication with Mr. Armstrong and his representatives and we understand that he does want to be part of the solution and assist in the effort to clean up the sport of cycling," chief executive Travis Tygart said in a statement.
"We have agreed to his request for an additional two weeks to work on details to hopefully allow for this to happen."
After years of denials, Armstrong admitted in an interview with Oprah Winfrey last month that he had cheated his way to a record seven Tour de France titles with systematic use of banned, performance-enhancing drugs.
Last year he was stripped of his titles after being labelled a "serial cheat" by the USADA.
Tygart then told the CBS "60 Minutes" program on January 27 that his agency had requested an interview with Armstrong while disputing the cyclist's claims of a clean comeback in 2009.
"His blood tests in 2009, 2010 ... one to a million chance that it was due to something other than doping," Tygart said.
In a letter to USADA on January 25, Henman said his client was willing to cooperate with the agency but that pre-existing obligations made the February 6 deadline impossible.
In that letter, Herman raised questions about the role of the USADA in ridding cycling of performance-enhancing drugs. He noted that "professional cycling is and has been largely a European sport".
Herman applauded the International Cycling Union's announcement that it would work with the World Anti-Doping Agency in a broad probe into the use of drugs and rely on a "truth and reconciliation" process.
"As such, we would like to make sure we coordinate with the truth and reconciliation process to examine the culture of doping in cycling in the past and to clear the air so that cycling can move forward," Herman wrote.
Armstrong, 41, said in his interview with Winfrey on her cable network OWN that the lifetime ban against him was like a "death penalty".
He added that he had no ambitions to return to professional cycling but would like to compete in sanctioned athletic events.