I did it a few years back over the Christmas Holidays, without much specific prep for it. I had done my first Ironman earlier that year, and my buddy and I decided we could get it done on the residual fitness.

A few tips:
-Start videos at 70%, and work upwards if you get to 5 and still think its too easy
-Change of clothes every few videos
-Plan out your nutrition in advance
-Save your favourite video for the end. We picked The Wretched because it sounded appropriate to put that last (we had never done that one), but I would have preferred one of the better videos.
-Alternate between types of videos (intervals, steady state, etc.)
-You get 10 mins between videos. Set a 9 minute timer each time you get off the bike so when it goes off you can use that as your cue to start making your way back on
-Do it with someone else if you can. Much easier to grunt through the last few when someone else is doing it too
-Plan your celebratory meal for afterwards. For me it was greasy pizza and beer.
-Have fun!