Lex's first episode of Doctor Who will be ep. 1 of Dalek Invasion of Earth. It's what I'm up to, and I'm waiting until he's home before I watch it. He will probably be asleep on my chest through it, but it counts.

Your next difficult decision will be how quickly you can show him episodes 4 - 6 of Star Wars, and how long you can put off showing him eps 1 -3.