The Perks of Being a Wallflower is a coming-of-age epistolary novel by American writer Stephen Chbosky, which was first published on February 1, 1999, by Pocket Books. Set in the early 1990s, the novel follows Charlie, an introverted teenager, through his freshman year of high school in a Pittsburgh suburb. The novel details Charlie's unconventional style of thinking as he navigates between the worlds of adolescence and adulthood, and attempts to deal with poignant questions spurred by his interactions with both his friends and family.

Answer this question: when does perks of being a wallflower take place? Let's give stream of consciousness first:
To answer the above question, the relevant sentence is: Set in the early 1990s, the novel follows Charlie, an introverted teenager, through his freshman year of high school in a Pittsburgh suburb.
So, the final answer is the early 1990s.