The best way to fit language study into a busy schedule is probably to get Anki or Memrise or any of the other flashcard apps for your smartphone (or even just physical flashcards, if you're so inclined) and use them to study whenever you have five minutes while waiting for the bus, at the dentist, etc. It doesn't sound like much, but if you make it a habit to use your downtime for something useful, you will be surprised how much time it adds up to. And this is not just for vocabulary, you can create cards to practice grammar like declensions or conjugations, too.