We stayed at 'The Plassey' Nr. Wrexham @ 5 years ago, back in the dark ages when we were still in a tent. Whilst quietly chatting with friends at 10.45pm, we heard a knock and saw a torchlight through the canvass, accompanied by a booming voice saying 'be quiet, I can hear you at reception!'. I've no doubt this 'warning' must have woke a few people up and not our low 'mumblings'.
On the other hand, I once approached a group of families that were still up and chatting at 1.30am, and asked them to keep the noise down. I turned and walked away before they had time to remonstrate, which was probably a good idea. On seeing them the next morning in daylight, the father was built like a brick sh*thouse!
The point I'm making is that campers always seemed more tolerant of late night noise, as a lot of activity goes on outside the tent in good weather. As for caravanners, a lot seem content to lock themselves away at 10.30pm and watch tv or go to bed. We're as guilty of this as the next family, but we still have occasions when friends come over and we'll sit outside in the awning and have a reasonably quiet chat after the barbie has burnt out.
Midnight would seem a fairer time to start keeping the noise down.