Tesla doesn't care how long we(model 3 reservation holders) hang around their store. If anything, they will encourage us on our happy day of picking up our car to stick around with big smiles, eat our cookies, drink coffee and check out what else is in the store while potential costumers are coming into the store possibly for the first time. Tesla doesn't want their staff having to hold our hands for 1 hour in order to take delivery of a vehicle. I would guess that they will schedule truck loads or train loads of pickups for the same day and have their employees prep the cars for pickup and only needing 5 minutes per car in order to talk with the customer and answer any questions AFTER the reservation holders do their own inspection.
Not sure how it works in Europe, and I suspect Tesla is a little different than most other OEMs, but what you've just described is what American dealers thrive off of in their showrooms.....when someone buys a car and is all happy, they honk horns and ring bells so that the perspective buyers in the room want that "good" feeling too.
Tesla's approach is probably slightly different, but the same desired effect is achieved.
They play off of the human "fear of missing out".