The paper focuses on body weight gain among immigrants in the US. The emphasis is on disentangling different time lines that are relevant in the context of immigration and acculturation, namely length of exposure to the high obesity culture, age at immigration, year of immigration and aging. Using data from the National Latino and Asian American Study (NLAAS), we find that (1) acculturation is associated with higher BMIs for the 1st generation, but not the 1.5 generation; (2) immigration at an early age (before 12) facilitates acculturation progress and drives BMI convergence to natives; (3) the effect of sojourn length in the host country is unstable across model specifications; (4) BMI differences between Asian and Latino immigrants are partly due to effect size differences in the acculturation variables.