ACUS.gov report says RR was Acting Attorney General for 1 day

"…Rod Rosenstein’s one-day of service (from government records) as acting Attorney General before the White House picked Matthew Whitaker)."

https://www.acus.gov/sites/default/files/documents/draft-report-acting-agency-officials-09162019_0.pdf

CALL FOR SHOVELS

https://www.acus.gov/research-projects/acting-agency-officials-and-delegations-authority

Administrative Conference of the United States did a project in 2019 on "Acting Agency Officials and Delegations of Authority" (Justice Scalia was Chairman 1972-1974)