When Does "Troop Beverly Hills" (1989) Take Place?
"Troop Beverly Hills" is a comedy film written by Ava Ostern Fries with Pamela Norris and Margaret Oberman that released March 24th, 1989. So when is "Troop Beverly Hills" set?
It takes place in the year:
We know this because in the first scene of the story Phyllis Nefler’s application to be the Wilderness Girls of America’s Beverly Hills chapter troop leader in the section for "Former Employers", under "To Mo/Yr", she has put down "3/87" for March of 1987 AD. So it is almost certainly after March of 1987 AD.

1990 AD
We know this because in the first scene of the story Phyllis Nefler’s application to be the Wilderness Girls of America’s Beverly Hills chapter troop leader in the section for "Former Employers", under "To Mo/Yr", she has put down "3/87" for March of 1987 AD. So it is almost certainly after March of 1987 AD.
More specifically, in the third shot of the entire movie a poster is seen reading: "WILDERNESS GIRLS Southern California 1989". The poster is then seen several times throughout the narrative in the "WILDERNESS GIRLS OF AMERICA SOUTHERN CALIFORNIA HEADQUARTERS". During a party at the home of one of the troop members, about two-thirds through the plot, Phyllis announces, "And next, it’s on to the annual jamboree where our girls will compete for the ultimate honor of being next year’s poster troop!" If the upcoming competition is to decide who will be on "next year’s poster", the current poster on display that clearly says "1989" must commemorate last year’s jamboree.
1989 + 1 = 1990.
Indeed, the second-to-last scene is the moment the photograph is taken for the new poster reading "1990" and capturing the event that has just finished.