If you like to go by the book straight to results, you can get up to speed within a month or so.
However if you try to create something unique and creative that no one has ever done so far, you will run into great trouble. Also if you try to learn everything in order to become master it will take forever.
Better to say “I WANT TO CREATE THIS” and write it on your wall and go straight to the results.
Examples of good tutorials to start:
Soda Can https://www.youtube.com/results?search_query=blender+soda+can
Package Design https://www.youtube.com/results?search_query=blender+package+design
Product Design https://www.youtube.com/results?search_query=blender+products+tutorial
Examples of wrong tutorials to start:
What exactly??? https://www.youtube.com/results?search_query=blender+tutorial
Why use it??? https://www.youtube.com/results?search_query=blender+compositing+tutorial
No you don’t want this… https://www.youtube.com/results?search_query=blender+spaceship+tutorial