I've learned that, just like exercise, you have to schedule songwriting (or any kind of writing). You can't take the attitude that's it's optional; something you'll do "if you have time". You'll never have time. You have to make time. It has to be scheduled, and you have to be "religious" about it. And you must defend it from all attackers--wives, kids, friends... but mainly from the enemy within yourself.
Yourself? Yes, yourself. My brother Greg, a writer and English professor, is grappling with this problem. Why don't you schedule time to write? Because, he said, "it seems self-indulgent rather than important and essential."
Of course that's nonsense, as he knows. If you're a writer--even a beginner writer, then it's important and essential for your happiness.
But like exercise, you need to set achievable, realistic goals. Maybe you shouldn't say "I'm going to schedule an hour a day". That's too big a departure from your current routine, so you could be setting yourself up for failure. Try something less that's more easily achievable. For example, 20 or 30 minutes, 3 days a week. You can increase the time later if you want. But regardless how short a time it is, it should be a regular schedule. For example: "On Tuesday, Thursday, and Friday morning I will write from 6:20am to 6:50am."
You'd be surprised what you can accomplish in 1/2 hour, or even 20 minutes.
I'm not a morning person, so getting up early 3 days a week to write just isn't going to happen. I know that. I work a day job, so after I get off work at 5pm, I go exercise on Tuesday, Wednesday and Thursday (also Saturday and Sunday). Then I take a shower, and write from about 6:30pm to 7:00pm. Then I have dinner. So I schedule both my exercise and my songwriting, one after the other. I also schedule a longer session on Saturday or Sunday afternoon.
Another thing I learned: don't set any goals or expectations for your writing period. For example, DON'T say, "I'm going to finish the song I started 6 months ago in this session." If you do that, you won't finish it, because you'll be feeling the pressure, and then you'll beat yourself up about it. The only thing you have to say is, "I am going to write during this time." If you schedule time and write, then things WILL get accomplished eventually.