How long to learn PostgreSQL?

I want to learn PostgreSQL and How to make the learning process efficient, but really don't know how long it would take even after googling my question. I used MySQL before and knew relational database. However, I would like to use PostgreSQL the implement my web back end database management system. I want sufficient knowledge to do it, design not ugly structure, write not ugly code, like I used MySQL for another web app project before. I am not asking the specific time, but at least I want a sketch in my mind. How much effort I need to invest? What kind of problem I would have? Any lessons you learned can be shared? Thank you very much!