The setting is an integral setting because it is a major plot point in itself.
Explanation:
The story "All Summer in a Day" is set in Venus and the plot is based entirely around the setting,
The people have to interact according tot he setting and the weather and society and the geography of the place all define how the story works.
Thus it is an integral part of the story in that it actively shapes the narrative to be what it is right now.
This is one condition for what the story means in terms of an integral plot setting.
All summer in a day in itself is a reference to the fact that Venus revolves around the sun that fast that there are summers that can last a day.
