This is actually a perfect application of GTD. Most people don't realize how flexible GTD is, and feel like everythin must be well define, and have a time frame. It doesn't. You have the reviews for that. You have the "projects" list for that. You have "waiting for" for that.

"Spending time on 'creative job x'" is actually a perfectly good task name to add to your "project" list.

In your daily review, you scan the one you want to work and and you add the ones you feel like to your "next" list.

GTS itself must NEVER be applied as-is, and should be adapted to your line of work, rythm, life style and personnalité. And it's very good at it.