One single pilot machine can have 2 pilots on board here is a quote from the B212 FM and it's the same for 204, 205 and probably any single pilot machine out there.
Left crew seat may be used for an additional pilot for VFR day and night operations when approved dual controls and copilot instrument kits are installed.
If there are 2 pilots in there, one can fly the outbound route and the other one the inbound route. Both of them can log the time they did.
When the words " you have control" is given, he becomes the new pilot flying on board.
If you are a pilot and YOU fly an aircraft you can log the time no matter what seat you are sitting in.
For multi crew aircraft is a different story.
JD