Do it whenever you can afford it. Sometimes, a steady income is just an amount with several digits added to your account while the time with your kid cannot be played back and it's the most precious.
I am just a newcomer to the road of a full-time mom and it has been around 3 mths since I quitted my job. Though I need to cut back because of quitting the job, I think I have made a very good decision. It's the happiest moment in my life....