The FO, should have noted the time and from that point forward claimed command pay and and logged as command time in the logbook.
Folks,
Again quite a while ago, a QF Captain was incapacitated, the F/O naturally became PIC for the remaining five or so hours of the flight, and sought so to do.
The then version of DCA/D0T/DoT-ATG/CAA/CASA ( I have probably left a few out??) said a very emphatic NO!!, because he didn't have a "first class endorsement", or ATPL, only a ATPL (2nd) with a "Second Class Endorsement to First Class Standard".
This was "back in the day" that a QF F/O doing a sector logged "dual", despite that being contrary to the Act, Regulations, ICAO , the CWA and probably the RSPCA.
So I guess that was five hours dual without an instructor, an interesting concept.
AAaaahhhh!! the wonders of aviation bulldust regulation/policy/bureaucratic buggery in Australia --- we are just so lucky to not be the same as the rest of the world.
As Malcolm Frazer said: "Life wasn't meant to be easy" --- and CAA/CASA took that as S.12 directive.
Tootle pip!!