When Does "Deenie" (1973) Take Place?
"Deenie" is a coming-of-age novel written by Judy Blume that released January 1973. So when is "Deenie" set?
It takes place in the year:
We know this because Wilmadeene "Deenie" Fenner tells us in narration she is about to visit a modeling agency and "The first one Aunt Rae read about in TV Guide.", a real-world magazine first published on June 14th, 1948 AD. So it must be after June of 1948 AD.

1974 AD
We know this because Wilmadeene "Deenie" Fenner tells us in narration she is about to visit a modeling agency and "The first one Aunt Rae read about in TV Guide.", a real-world magazine first published on June 14th, 1948 AD. So it must be after June of 1948 AD.
More specifically, Deenie informs us at the very start of chapter one that, "My mother named me Deenie because right before I was born she saw a movie about a beautiful girl named Wilmadeene, who everybody called Deenie for short." and, soon after, "I really liked it, especially the scenes between Deenie and Bud. He was this guy who was madly in love with her." In between, we learn, ..."it took me almost thirteen years to find out what really happened to the Deenie in the movie. She went crazy and wound up on the funny farm." This movie is "Splendor in the Grass" (1961), which released October 10th, 1961 AD. She goes on much later to say, "A teenage model has to make it by the time she's seventeen if she's ever going to make it big. So the next four years will be very important to me." so Deenie is indeed 13-years-old, making it 13 years since the movie was in theaters.
17 - 4 = 13
and
1,961 + 13 = 1,974.
Specifically, Dennie’s narration also says, "But today it was warm and sunny, just the way it always is in September when you're wishing it would hurry and get cold." strongly implying it is September of 1974 AD.

