I schedule it in.
Right now, I schedule it in at night. So, at 9pm it's my time to scrap.
However, I start earlier! I read the challenge when it's posted, and think about it. I'll think about the photo I want to use, and the kit I want to use. If I have a chance earlier in the day, I'll grab the photo and get it ready. So, today, after reading about the dispersion technique, I figured I'd want an action photo. Then I thought about doing a rainy day photo. In the end, as I was grabbing a photo a different one came to mind and I used it.
For me, the photo and kit are the part that take the most work! So I try to get going on those quickly even if it's just in my mind.