Almost every INTP I've ever known was obsessed with time travel....
Yup. I agree with that. Here are some quotes from Donnie that tell me he's very much INTP and since the movie is titled Donnie Darko...I think it's quintessential INTP.
Here are some quotes from the movie:
Dr. Lilian Thurman: Do you feel alone right now?
Donnie: Oh, I dunno. I mean I'd like to believe I'm not but I just... I've just never seen any proof so I... I just don't debate it anymore, you know? It's like I could spend my whole life debating it over and over again, weighing the pros and cons and in the end I still wouldn't have any proof so I just... I just don't debate it anymore. It's absurd.
Dr. Lilian Thurman: The search for God is absurd?
Donnie: It is if everyone dies alone.
Donnie: Life isn't that simple. I mean who cares if Ling Ling returns the wallet and keeps the money? It has nothing to do with either fear or love.
Kitty Farmer: Fear and love are the deepest of human emotions.
Donnie: Okay. But you're not listening to me. There are other things that need to be taken into account here. Like the whole spectrum of human emotion. You can't just lump everything into these two categories and then just deny everything else!
Those are just two excerpts...but mostly everything Donnie says questions reality or what is perceived as such. Or he is trying to clarify the ideas of his friends (smurf dialogue) and/or his teachers. He questions everyone and everything to get a deeper understanding.