It is difficult to generalize since it depends on the learning capabilities of the individual. I can share from my experience, it took me 3 months to learn all the skills required for a frontend developer.
I spent 10 days learning the basics of web development, responsibilities of front end developer, backend developer, which tools to learn and preparing the best learning path for me. Around 30 days to learn basic technologies like HTML, CSS, and JavaScript. Spent 20 days on getting familiar with the sublime text, photoshop, etc. Final one month I spent totally on implementing websites and applications on my own. Follow active bloggers who write on frontend development and keep yourself up-to-date.
I strongly recommend this full stack developer course by Intellipaat if you want to learn both frontend and backend development.
You can watch this video on Frontend developer career path for a detailed explanation:
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