As a designer you can earn relatively fast and easy , provided you have a creative eye , some marketing knowledge and get intimate with the front end languages of websites.
As mentioned above there is such an extraordinary amount of talent when it comes web developers ( well in my eyes ) i wouldn't bother saying i am one unless its on black and white. I can do alot of development but i avoid anything serious. Its also a field of very very high standards by nature. This is just the type of people good developers are.
I dont think you need a degree ( although recommended i agree ) there are too many free lancers like myself , and people by nature the clients are looking for cheap developers , so they hit up students , freelances and so forth. Many freelancers however do not draw the line where they say this is out of my scope , anf end up producing problems , in their product and the name of the industry as a whole....dont be that guy.
Time frame depends on you competency to solve problems, you network , time spend actually practising and of course tools for learning.
Quite honestly if its not something you want to get serious about , i wouldn't bother , there are easier ways to make a little money online that doesnt require this much intellectual investment.