There is one referenced on their homepage. On average, 34 hours of study in the Spanish course would be equivalent to a full semester of language education in c

There is one referenced on their homepage. On average, 34 hours of study in the Spanish course would be equivalent to a full semester of language education in college. For me that would be about a month of practice. I have seen the effects myself. After a month or so, even though I had learned some spanish before, native speakers suddenly slowed down (in my perception). An important clue: Use the "Strengthen your skills" button frequently to keep the tree golden. Duolingo itself doesn't nag you enough to do that, but it's essential for mastery of the language.