Mueller Report, page-100

He's willing to go in front of congress with 5 mins for each member but not in private for 30 minutes from each parties commitee counsel. (lawyers).

"In addition to five minutes of questioning for each member of the committee, Rep. Jerrold Nadler (D-N.Y.), the chairman of the committee, has proposed a round that would allow for each side to question Barr for 30 minutes, a source said. That round of questioning also would allow the committee counsels for both parties to question Barr.
Nadler also has proposed having the committee enter a closed session to discuss redacted sections of special counsel Robert Mueller's report, the source added."

https://thehill.com/homenews/house/441018-barr-warns-house-dems-he-might-not-appear-at-hearing-report

He is the AG and has no reason to answer questions from unelected counsel, especially as he's not under investigation of a crime.