Once had to spend 8 hours in the Aer Lingus lounge at DUB which I entered with my PP. (Due to delay incoming, missed outbound flight by 10 minutes at 6:50 am. EI would not put me on an IB or even Ryanair flight so went out at 16:30).
When I entered the lounge, my boarding pass was checked and the entry time was noted, and I was told “you’ll have to leave after three hours.” I spent the entire day in the lounge, through shift change of personnel, changeover from coffee and tea to beer and wine, morning biscuits to afternoon (rather poor) finger sandwiches…At times I was the only one in the lounge. Had to pass the registration / greeting desk at times to access the toilets, which are outside the lounge.
Did not hear a peep about leaving the lounge, or even a question about “when did you enter, sir?”
If you keep reasonably quiet and keep your feet off the chairs – that is, remain unobtrusive – and have a bit of good luck, I think you should be ok.
Worst case scenario, you pay twice.