I'm listening to a file which has no introduction but there are both Subliminal and Binaural versions also.
I would listen to the regular version, if it has audible words. It should work better.
Does the Subliminal also contain brainwave entrainment
Send a message to the author. They might be the only one that knows this.
What effect should I have from the Binaural ?
A binaural typically helps you to drop deeper or align your brainwave closer to the audio wave pattern (which generally boosts effects)
Is there an optimal time to listen for best effect?
It depends on the person. You might have to find your own optimum time, like maybe before bed (but not during sleep. I wrote an article on TransformHypnosis about why you shouldn't do that)
But typically, the best time to listen is now.