Learning AI is never-ending but to learn and implement intermediate computer vision and NLP applications like Face recognition and Chatbot takes 5-6 months.
First, get familiar with the TensorFlow framework and then understand Artificial Neural Networks. After that, learn deep neural networks, Convolution Neural Network, Recurrent Neural Network, and Auto Encoders. You can check out TensorFlow official documentation to learn how to build basic AI applications like Image Recognition, Text Classification, Neural Machine Translation, etc.
You can check out this Artificial Intelligence Training program to learn AI concepts and implement AI applications.
Also, watch this video on AI: