We've all been there: You want to write, your characters keep you up (or wake you up) in the middle of the night showing you awesome scenes that you're desperate to type up. But, oh crap, you've got to get up for work in three hours, so you better not stumble out of bed unless you're pretty much awesome at pretending you're not groggy while at work. So how in the crap can you get writing done when life gets in the way?
Find motivation, wherever you can get it...and I can't stress this enough: At the times it will help you most.
If you can squeeze in 30 minutes of writing time when you get home from work, make sure you do something that will help you get in the mood. Whether its driving home in an eerily quiet car as you think of your characters and picture a scene you've been wanting to write but haven't figured out the details yet; or maybe you want to blast the crap out of your sub-woofers and sing at the top of your lungs to a song that helps you visualize your characters/book. Just do it. That way, when you get home, you're feeling that undeniable pull toward your computer/laptop to put those fingers to the keys.
Here are some things I do to help me get motivated (obviously depending on the story I'm writing at the time):
Listening to music
Listening to an audio book
Reading a book
In my experience, finding the right kind of motivation can be one of the most beneficial things to improving your writing craft. If it helps draw you into your story (whether you're writing or editing it), how can it hurt? In fact, it could enhance you're emotions so much that you actually improve what you've previously written.