For the record, the 1.5-hr limit reads like a recommendation, "as a courtesy to fellow flyers" or some such. I would hardly call it official. Who knows how it would be enforced if it all.
On a related note, this blog post was delighted to announce earlier this year that "...there's still no time limit on the cabanas, so once you grab one it's yours until your flight leaves." Was it really understood that you were entitled to camp out indefinitely?
http://www.ausbt.com.au/first-look-p...unge-hong-kong
CX advertised the Cabanas as a place to rest. They even provided a sofa bed for you to sleep in. Surly it isn't too hard to infer that CX welcomes pax to enjoy the room, and nap, till your flight time.
I'm not against having time limit when there's a queue, but it should be clear and official, not as you said open to interpretation. If it's voluntary, fine, please don't knock on the door and asking a person to leave because a guy is yelling and screaming about wanting to use a cabana in the lounge.