Well, for web development a solid understanding of HTML and CSS is a must. You can easily learn HTML within a month or within a couple of weeks depending on your dedication. HTML is the language used by the browser to read. CSS is very complicated but you don't need to know everything to make a good looking site with HTML and CSS. CSS will take a couple of months to learn as well. Next is Javascript. JS is the language used to do web programming. JS is a must to provide a rich experience for the user. The best example of a website that utilizes JS extensively is Twitter. JS can be very complex to someone who has no coding background. However, there are tons of free tutorials on the internet and you can learn the basics of JS in a couple of months and to "Master" JS, it will take at least a year. Again, this depends on your ability to understand and learn fast. Once you have mastered these three languages, you are known as a front end developer. FED, is basically a developer who has the ability to create interactive web applications using the aforementioned languages without any DBMS. (Database Management System).
If you want to become a full-stack developer, (An individual who has the ability to build complete web apps. Both front end and backend) you need to learn backend development as well.
For backend development, you need to learn languages like, PHP/Python/Java/Ruby This will also take some time but in my opinion, becoming a full-stack developer is an extremely valuable skill given the day and age we live in. If you need any help, feels free to drop me a message via discord or pm.
Good luck.