To be a successful freelancer it's important to know how and when to juggle assignments. But more importantly you have to know when to say "NO" to an assignment.
I knew that my delivery dates for these 3 assignments are well spaced out, but they all needed to see something to get the ball rolling. If I run into an assignment that has a due date that would be difficult to hit because of my current assignments, I would turn it down.
Now don't get me wrong... I hate turning down work, but I would hate to miss a deadline even more. I don't mind working late at night or on the weekends... that's the life style of a freelancer, but as a successful freelancer you have to protect your reputation. Delivering an assignment late is one of the worst things you can do. Miss a date you will lose a client.
Bottom line: Don't take an assignment if you feel you can't juggle your workload to make the date it's due. You are not doing anyone any favors if you miss a deadline. Successful freelancers are on time all the time.