Duolingo is a system of small steps. Short lessons are divided thematically. How much time is devoted to learning per day is up to us. The application has an interesting motivational system and allows competition between friends, making learning even more interesting. Advantages are: free, intuitive, fun learning, adapted to the user's level.
If you are an app freak, it's good to use different applications to learning English too. I will show you many handy apps to keep learning English in a few minutes. Furthermore, I will show you many online dictionaries and websites to learn languages.