Both my Maroon clowns were juveniles when purchased, about six months apart. Went through the harrowing pairing experience & once that was sorted out, the original clown becoming dominant, it (she) put on a rapid growth spurt. Doubled in size in a matter of a couple of months. After that it took about two years until the first spawning event.
Not sure how much variance there may be in this time line for other species of clownfish, but seems like yours are already paired, so you've got that part aced. May also depend on other factors such as water parameters & surroundings. Mine have always had a BTA to host them, but I'm not sure that will speed up the spawning process. Many breeders simply provide an empty terra cotta flower pot for their clowns to breed in & it seems to work fine.