I charge 2/3 of my incall rate, but I rarely do social only dates. It tends to be an addition to private time.
I have one client I see almost every week for 3 hours. He comes to my place, we just chat or eat food, no sex, he pays £300. I'm happy with this as it's ways at a time when I wouldn't readily be knocking back full rate bookings. Plus, it's very little effort.
For an 8 hour booking, I'd charge £800, especially if you are spending time travelling to the event.