If you are doing Mango, Duolingo or Keewords, I suggest 15-30 minutes a day depending on age.
Mango — through libraries, 16 languages — easy paced, guided lessons, teaches conversation through phrases
Duolingo — a handful of languages done with interactive activities
Learn 101 — Beginning vocabulary and grammar for over 100 languages
French Beginners Lessons — youtube channel, half a year’s worth
Spanish Beginner’s Course — flashcard system with quizzes
American Sign Language (I recommend doing this in addition to a spoken language if you think you are headed to college. You’ll need to check with your school district and any colleges you are interested in as to whether this would count to meet any foreign language requirement. If a college you are looking at asks for a “world” language, then sign language and things like Latin would not count to meet their requirement.)