As I said, with a shared cinematic universe, it's hard to tell. Sometimes characters show up before their own movies, like Black Panther and Spidey in Civil War or Wonder Woman in Batman v Superman.
Personally, I'd prefer it if they introduced the FF in earlier movies before they got their solo film. So far, of the four existing FF movies, the least dire one is Rise of the Silver Surfer, the only one that isn't an origin story. The FF's origin story is the least interesting thing about them. They're more interesting as established heroes, the royal family of the Marvel Universe, the ultimate scientific think tank that everyone turns to with their problems. So it'd be cool if several earlier movies seeded the idea that they came to prominence during the five-year gap, basically filling the role in the MCU ecosystem that Tony Stark had vacated after Infinity War, and thereby set up a solo movie where they're already established, veteran heroes and scientific authorities. I do not want to see yet another stab at their origin.
