Depends on what your feeding it,mine grew pretty quickly upto 8" then stopped then grew in a spurt again to 12" .
Cant remember how long but less than a year i think?
Took me 9 months for my endli. Little longer for the ornate. Every bichir is different though in my experience. I feed a lot of whole tilapia and krill and worms and massivore.
Less than a year for me. I'd say about 9 mo. Strictly eating pellets, sinking cichlid and massivore/carnivore. My Ornates are growing slower, still @ 10'.