Well, that's not quite the question. I decided to throw caution to the wind and eat lunch in Ikea today. I had brought things for DD and I also gave her peas etc from my plate. I ate my lunch and she ate some of hers, squished some, threw some etc etc and she was still squishing when I had finished. How long do I sit there before starting the long task of sweeping the floors? I don't want to sit there all day while she arsesabout finishes but I don't want to stop her if she is actually still eating. Problem is, as I'm sure everyone finds, it's quite difficult to tell when they are finished as I'll start to clear up and she puts things in her mouth again!
Tonight was easier. She took the lovingly prepared plate of pasta, cucumber, tomatoes etc and threw them one by one onto the floor
As long as it, takes you to eat your lunch, drink a hot drink, and investigate the current chocolate possibilities. Feel free to add 'dessert' to the tray at a point that suits you, without necessarily removing anything.
Throwing stuff on the floor is an important step apparently as they all do it for some time
I found with dd2 that once she started to throw/drop stuff on the floor that she had finished eating, so once that started to happen, then the meal was over. Like your DD, she did it one by one, still does, once she has finished eating. You can always give her the plate back if she looks remotely like she might eat any of it