Not likely that time of day has any effect on an interior lighting. As far as i know the CK only simulates light in a static state while the game's lighting is animated.
If he's set those various things to an external emmitance, and the time is different ingame then when he was looking at it in the CK that would cause this.
Other than that things should look more or less rightn on. I don't think the CK does
full lighting like the game, but it does the important stuff. Otherwise designing levels would be impossible.
My money is on emmitance and different time of days. (In CK is 10am, ingame looks like night time)