Ok, there was a topic about this on the forum before.

And I have tried to record a wav file to say "Lucic83 , you are dreaming"

I only tried once and I did it every 15 minutes for about 30 times during the night so that would be like 30 / 4 about 7 hours total.

Try it at a low and then increasing volume and see what you get. This was tried in a lab and it worked for the experimenter.

Stay Lucid!!