I have always found the fun of the overnighter to be in the lack of structure, unlike shorter dates where everyone is somewhat painfully aware of the plans and timeline.
Most extended dates that I've been on don't end up following the initial plans and that is where I find most enjoyment. Over the course of the evening you may plan on going for dinner, theatre, etc. but then when you get together you'l find that time just seems to slip away from you and plans fall by the wayside as you get lost in all the little pleasures your date can offer.
Waking up and seeing the sunlight shining on a bare leg stretched across your bed, seeing her in your dress shirt as she touches up her makeup (which you messed up a few min. before in your bed) just before you head out for a nice meal, seeing those beautiful blue eyes stare across the table at you knowing that in a few hours those same eyes will be looking down at you as you taste what is now hidden under her fitted black pencil skirt.
At least for me that is what the extended date offers that others cannot, the tease, the mental attraction, the opportunity to relax and enjoy the real person, something that isn't always possible when you meet for only a couple of hours and something that can't be planned. It's spontaneous and fun, exploring the natural chemistry that is between you.