Until you're one of the lucky few who get to call writing their full time job and earn an income that allows you to keep it that way, you'll have to manage your writing time with your day to day life. As someone with a full time job, spouse, animals, and a budding writing career, I can tell you this is no easy task. I know people who have quit writing because they just couldn't find that happy balance of time. How does one avoid such a sad end? That's going to depend on you, your family, and how bad you want to write.
Like many of you out there I lead a very busy life. For the most part I can't stick to a writing schedule because I never know when I'm going to have time. So how do I do it? Sometimes literally one minute at a time. I don't set my goals so high that I have to have hours to write. I'm happy if I can sit down for five minutes and write a paragraph. Progress is progress, no matter how small. You have to take what you can get. Whenever I can I try to plan on writing first thing in the morning as I do my networking (Twitter, Facebook, e-mails). I literally write between pages loading. This won't work if you're blessed with fast internet service! I'll admit, it's not the best way to write, all distracted and such, but it works. Once I'm done networking-set a timer for this folks, you'll thank yourself later-then I enter everything I hand wrote the day before into my computer. I carpool which allows me to take a notebook and write all the way to work. Whenever I can I also write during my breaks at work.
None of us have time, not in today's world. The key to getting your writing done is to steal time. Try to write while the kids are napping or take a notebook to their soccer practice. Write any time and anywhere you can. Best of luck!