Which detail in the excerpt supports the idea that the narrator and his cousin spend a substantial amount of time together

Hi. You did not provide the story that your question refers to, nor do you present the excerpt that the question asks to be analyzed. This makes it impossible for your question to be answered. However, when searching for your question on the internet, I could find another question exactly like yours, which showed that it referred to "A Christmas Memory," a short story written by Truman Capote, but unfortunately, that question also didn't show the excerpt, which prevents me from being able to present you with an exact answer. However I will try to help you as best I can.

We can see that the narrator of this story spends a lot of time with his cousin, because they spend the entire Christmas day together, doing various activities. This narrator is called Buddy and in this story he tells how he and his cousin spent Christmas day talking, flying kites, decorating the Christmas tree and baking cakes to give to strangers on the streets. These activities made them spend a lot of time together and they loved it to the point of repeating them every year.