I'm a firm believer in learning by doing so I'd say you should begin as early as possible.
In those stages, knowing how to search is important. Try to understand the problems you deal with and look for features and/or tools that solve them. Get to know the documentation and surf through Q&A sites.
That's how I've been learning since I started in college and it's served me well throughout years; move fast and break things, as they say. Just be careful not to release/publish anything broken.