Can you write poems out of thin air or do you need a lot of time to think it through?

I've got poems that took weeks to write. Then I have some that took minutes. Out of the ones that's been published, 50% have been the ones that were written with little effort. I think those are the ones when I connected with my muse instantly. Other times I have to struggle and rewrite, revise, rewrite, revise. Guess my muse is finicky.