If what Gwen said above is true, and, in my experience, it is, then the answer is no - we can't totally control when inspiration strikes. And that means that when it does, we must be prepared to drop our plans and follow it.
So let's summarize my hypothesis:
If, to maximize your chances of creating great art, you have to pursue inspiration every time it strikes and, if you never know when it's going to strike, then, to produce great work, you will, necessarily have to "blow off" some tasks if you want to take advantage of that inspiration.
So you tell me - when inspiration does strike, should you head to the studio and start creating or should you run errands?
And the funny thing is, the more you create, the more it happens. It's a self-sustaining feedback loop. So, for those who do great work, inspiration strikes a lot. [2] Therefore, a lot of the stuff creative-types "should" be doing gets "procrastinated." And the more creative one becomes, the more likely the other things (the "small stuff") are to be put off.
And, consequently, the rest of the world thinks that artists are "flakey."
But now you know that's really a compliment.
Until next time, please remember that Fortune Favors the Bold Brush.