Dr. Craig is a liar.

[SteveII]

Craig is asserting that 1) God was timeless and unchanging prior to creation and then, 2) God enters time and becomes temporal at the moment of creation.

This is a prime example of sophistry if ever there was one. You start by imagining a God existing before the universe, incapable of thought, or action, or change of any kind, and then imagine God suddenly thinks, and acts, and changes, deciding to create the universe and time. No matter how hard you or Craig try, you can't avoid these stages of transition (a.k.a. Time): Before creation -> The Moment of creation -> Post Creation. God's imagined corresponding stages would be: Changeless/Timeless -> Changing to actualize Creation -> Temporal with the universe. In other words, a timeless state prior to time is self-contradictory, because, by identifying that the timeless state existed before time, we must necessarily place it in time, on a timeline.

This just isn't rational.

That's why your own thoughts on the matter are so contradictory... because it is logically impossible for any sentient being to do anything from a truly changeless, timeless state - including changing the timeless state itself! Your own instincts imagine God must have had "a series of mental events [forming] a before and after (therefore some measure of "time")." Your mentor Craig would completely disagree with your line of reasoning - even though his own disagreement is wholly irrational.

On the other hand, if "God existing idly before creation" is just "a figment of imagination," and "prior to creation there literally are no intervals of time at all," then God and the universe would have begun to exist at the exact same moment! Goodbye special pleading from the Kalam! Absent any moment prior to creation, there is also absolutely no point in arguing for a "timeless, unchanging" state of God, because God's existence would have always been temporal with the universe as there could be no "before," and thus no time for anything, including God, to be in any state - timeless or otherwise. (Q: How long did God's timeless state last prior to the creation of time? A: Zero seconds.)

Now, why must Craig defend such a ridiculous proposition as a timeless God "existing changelessly alone without [before] creation?" and in the same breath asserting "prior to creation there literally are no intervals of time at all" (and thus, no before)? Because he knows, absent this concocted, self-contradictory absurdity, God would himself confront the infinite past regress of events (like the "series of mental events" that you imagined) which Craig asserts is anathema to his philosophy. So Craig attempts to counter this with a preposterous proposal - imagining a timeless, changeless deity existing alone, "timeless without [before] creation and temporal subsequent to [after] creation." And yet, Craig gives God literally no time to exist prior to [without] creation. Can you say "cognitive dissonance?"

Why do you think God needs to "think" about anything prior to creation? 
Why can't causation be simultaneous with its effect? Why does causation presuppose the existence of time? 
Why can't God become temporal the moment there was something to have a temporal relationship with?

You misunderstood the sentence: "The image of God existing idly before creation is just that: a figment of the imagination." The point was NOT to imagine God sitting idly.