That's not usually the case in a high-end sushi place. The chef will prepare your orders one by one and serve them out as soon as each is completed, so you will get one piece at a time.
I too am looking for the answer to this. Like are you supposed to eat the entire roll in 30 seconds? You're not even tasting it at that point. I'm hoping 30 seconds per piece.
The guide is probably specific to nigiri sushi, that's what is depicted at least. As the other commenter mentioned: in high end sushi restaurants, the chef will serve you individual pieces of nigiri sushi as you order them, so 30 seconds seems like a reasonable time limit in that context.