When was Tyler created?

Hi everyone, it's my first topic here.
I've just finished reading FC for the second time and I was paying more attention to details. It's not majorly important, just something I'd like to read your thoughts on.

Tyler manifests himself when the Narrator falls asleep, right? And he gets the feeling he never fell asleep, so he thinks he's insomniac.

But when was Tyler really created?

I don't think it was at the beach. In that chapter, the Narrator says "Tyler had been around for a long time before we met". When Tyler appeared at the beach, it was the first time the two personalities actually met, I think.

Apart from that quote, I think it would make sense for the Narrator to become Tyler beforfe being aware of his existence. Tyler may be a split personality, but he's a "person" like any other: he needed to establish contact with other people, get a job (the projectionist gig), find his identity, however well the Narrator had it defined in his subconcious.

Prior to the present story, the Narrator thought he had been suffering from insomnia for two years. This would mean Tyler had been around for two years, which would make sense if you believe what I wrote above.
But then, the Narrator started going to support groups, and he said he started sleeping again. What does this mean? Was he Tyler when he was asleep anyway? Did him sleeping well mean that Tyler was happy or something? Or was going to support groups and "losing all hope" some kind of Tyler-inhibitor?