Where did you come up with that?
An SIC is assigned for the entire flight and the other guy or guys are IROs.
Everyone I work with logs SIC for the entire flight whether they are in the bunk or in the seat

That is the way we do it on augmented crews on the B744!

The gist I got from another forum was civilian three piloted crews log all time as either SIC for FO's and IRO's, or PIC for the Captain.

If I logged my P-3 Special Crew Time (bunk time) in this fashion, it would add 600 hours to my total time.

Logtenpro won't let me log more PIC time than total time (I put Total Pilot Time into my Total Time column and left out Special Crew Time), so I have a note to add another 176 hours to my METPIC time.

Big deal? Not for TT, but when I count all of the Aircraft Commander (PIC) time from my P-3 days, the METPIC in aircraft over 12,500 lbs comes to 1030 hours. So those 9 hour flights of which I was PIC were logged accordingly: 6 Total Pilot, 3 First Pilot, 3 Copilot, 3 Special Crew, 9 Aircraft Commander.

I can clearly justify this following the Part 1 definition of PIC, but logging 9 hours of SIC time on 9 hour flights I wasn't AC, gets murky.

I can see how someone just below the TT threshold for a company would want to log military three pilot crew time like augmented crew civilian operators. Maybe checking with a sponsor who works at the desired company would be the best approach.

For us as augmented crews on the B744, we are all Typed on the aircraft and required for the flight. So just like the PIC is required, he still logs the entire flight even when he is in the bunk and so do the two FO's.

B-744: If i'm on a 9-hr flight, 3 operating crewmembers, I log 6.0 hrs (& note that TT was 9.0)... If on 13-hr flight with 4 operating crew, I log 6.5 hours (& note that TT was 13.0). I don't log bunk time.

As you can see, there are many variations on how to log the time!