Getting proficient with the fundamentals of React will usually take between 1-6 months. However, the precise duration to master React relies on your previous software development experience as well as the time you want to put on for the learning. It all ultimately depends on your speed to grasp the React concepts, the related understanding, and gaining skills to implement those concepts.
Certain React online courses last only for 3 weeks. In any of such courses, when you just invest a half-hour each day, you can easily master React JS. Moreover, it helps you to learn the advanced technologies in this field.