When the super is below the starter board, on the bottom board, with the field bees and with the grafted cells, the only connection with the queen is by air through the netting in the starter board. Thus they are in a queenless state as the queen is above the starter board in the first two days.
During the first day the bees in the starter box on the bottom board establish their queenlessness and collect many field bees.
The next day they are ready to get the grafted queencells in their queenless situation. The field bees trigger a high acceptance of the grafted cells. But they should not stay in this queenless situation with many field bees and few nurse bees.
The nurse bees are with the brood and the queen. The field bees are bad nurse bees and will finish the cells poorly. Therefore the next day after grafting you put the broodbox(-es) with the queen and the nurse bees are back to the bottom board again. Above an excluder on the brood boxes now come the super with grafted cells (and the field bees), the starter box.
The field bees will go down, sense the queen and be happy again and go out and do their field work. The nurse bees will sense the queencells and go nursing them. The excluder is necessary to create a situation where the pheromones of queen have difficulties reach the box with the started queencells as the queen can’t go there. Thus the nurse bees up there continue to feed the queen larvae as when there they sense the queen is poor as they don’t get as much queen pheromones, due to the excluder.
The nurse bees will finish the cells so they are well fed, which is the important thing, not the size of the queen cells (for example are long cells bad cells as the larvae then gets a long way to feed). If the weather is bad, the bees might eat up a couple of cells. They might even not feed some enough and those will stay open longer, maybe not be capped at all. maybe if the accepted number very high to start with.