Nah, someone else posted a video that goes through it in detail. The pre-rinse is 10 mins (depending on dishwasher) of splashing plain water around and around to get the grubbiest bits off, then it dumps the prerinse water and gets clean water for the main cycle where the detergent goes in.

One of the key tips in the video was to add detergent in the prerinse detergent section (some open section that lets it go in straight away), or if your dishwasher doesn't have one then just straight on the door or in the bottom. Just a small amount so the pre-rinse cycle has detergent in it so can get more off before the main cycle.

The only thing I've found about putting dishes in dirty is that some fancy dishwashers on the "auto" setting will sense how dirty the pre-rinse water is and set an appropriate wash cycle. If you've pre-rinsed, then it won't find much and will put it on a light cycle. This can lead to dishes not being clean if they are actually really dirty but you rinsed off the loose stuff already. But it can be worked around by just setting the cycle instead of leaving it on auto.

The QI monkeys are just buzzing around on the net finding factoids for the show, you can often find untrue or misrepresented ones.