Question: how long from ltjg to lt?
Answer: While there are no guarantees of promotion within officer ranks, based on my experience, it's about 2 years from Ensign (ENS, O-1) to Lieutenant Junior Grade (LTJG, O-2), and 2 years from LTJG to Lieutenant (LT, O-3). Often, a LTJG is “frocked” to LT about 6 months early before the appointment (promotion) is permanent.