So since 2015 we've learned that Hasbro plans to expand the Transformers films beyond the main series, creating a writers room in which the writers would plan out the upcoming years of Transformers films and make sure everything fits together, so far we know 3 of these films consist's of this year Transformers: The Last Knight, 2018 Transformers 6, which will center on Bumblebee, which will be the first film not helmed by Bay and 2019 Transformers 7, whose plot details and director are still unknown, so there was an IMAX Transformers fan event in which they showcased 30 minutes of footage of Transformers: The Last Knight, and the footage showed seemed to hint at Bumblebee past, so it brought into question if the upcoming Transformers 6, which will be directed by Travis Knight would delve into the backstory of eerybody favorite Camaro.
If Michael Bay interview with MTV is any indication, it seems the film will indeed be set before Transformers: The Last Knight or even before Bumblebee meet Sam Witwicky in the first film, this is what Bay said when asked about the film "It'll go a little younger, and it will deal more with his character and it's just about him." and when asked when the film fits in the timeline, he simply said "Back".
How far into the past the movie will be set is unknown at this point, but looks like we wont have to wait much longer for find out. as My Entertainment World revealed the film will start shooting in July.