Balancing writing with your day job

Today has been a really good writing day for me. The words have just been flowing steadily for a few hours now. I may have mentioned that I'm rewriting most of the first half of Water Magic. I'm now 18,350 words into the rewrite, and it's looking really good—way, way better than my rough draft. And I seem to have reached a balance between my household tasks—running to the grocery store, tidying up, exercise, laundry, cooking, wedding planning—and my writing time.

Problem is, not every day is like that. There's this thing that gets in the way—I call it my "day job." And as far as day jobs go, it's not so bad. I work in a library, hanging out with the books and the people who like books and the people who need me to help them find books. Which is cool. But when I spend a full day at work, including the 45-60 minutes of travel each way to get there and home, I'm really, really tired! So tired that sometimes when I finally get home and settle down on the couch, I open my WIP and just stare at the screen for ages, trying to will my brain to think of something clever for the dragon-speaker to say (or the sorceress, or the brownie, or the water spirit). And sometimes I can't do it. I'm just too exhausted. And that makes me feel pretty bad. After all, everyone knows that writers are meant to write every day. One of my favorite authors once told me that in person.

So I've been trying to think of ways I can keep to the "write every day" rule even on days when I'm working, or just have a lot of things to do. Susan Sipal from Harry Potter for Writers (an amazing blog that you should be reading if you love Harry Potter, especially if you're a fantasy writer) suggested getting up an hour early and getting some writing done in the morning before work. I think that's a good idea, but with my level of sleepiness in the mornings I'm doubtful that I could stick with it. Another idea I had was to take my writing notebook to work with me, and outline/work on the chapter I'm focusing on that week during my lunch hour. I normally reserve that time for reading, but I could read when I get home instead.

I don't know. Do the rest of you writers struggle to find a balance between writing and other commitments? What time management strategies work best for you? I'm going to be searching for a second job at the end of the summer, which will make my schedule even fuller, so I'm in desperate need of advice!