The deadline for Barton to accept or deny the charges had been 6pm on Tuesday night but the FA extended that to 12 noon on Wednesday following a request from the Rangers captain's representatives.
The FA said in a statement: "The deadline of 6pm on Tuesday 15 May, which Joey Barton had until to respond to the two FA charges against him for alleged violent conduct has been extended to 12 noon on Wednesday 16 May following a request from his representatives.
"The charges against the Queens Park Rangers midfielder are in relation to Sunday's match against Manchester City at the Etihad Stadium.
"Following the player's dismissal in the 54th minute of the fixture, there followed two incidents involving Manchester City's Sergio Aguero and Vincent Kompany.
"As Barton had already been dismissed, both of these incidents fell outside of the jurisdiction of the referee."