In HKG SO log P2X time for only when they are in the seat (even though the company expects those watching from the back seats to be involved in the operation and monitoring).
I recommend you ask your local aviation authority how the view P2X time and what time you can log in your non-HKG logbook - many countries log total flight time, not just seat time.
Some airlines now accept P2X time as valid time when interviewing (supply and demand) - ask the real airlines you may wish to work at how they view P2X time.
You don't want to under log your time. CX can be useful for gaining some SIM experience and even some P2X time prior to getting the job you really want.