I agree 100% with everything patio11 had to say. There is real fear involved when you have these low periods. Just because you're overwhelmed with work now doesn't mean you will be four months from now. But you should definitely celebrate the fact that you've proved to yourself you can get clients to pay you!
I don't think your only options are to quit your job ASAP or wait for 6 months. Instead what I'd suggest is redirecting all your extra freelancing income to a savings account (bonus points if its an account opened up for your business). Save enough to make yourself feel comfortable with the idea of a contract potentially dropping out of nowhere and not being able to find work for three weeks.
Once you hit that amount in savings reevaluate. Are you still getting enough work? Are your past clients going to give you great word of mouth referrals (which is one way to switch off of Elance)?
The big thing is you don't want your emotions to control your business decisions. I actually wrote a whole blog post on 'How Savings Impact Freelancing' http://challengeacceptedhq.com/how-savings-impact-freelancin...
Good luck and congratulations!