1. Attraction > lovers > love > friends
2. Friends > love > attraction > lovers
3. Attraction > friends > love > lovers
4. Attraction > friends > lovers > love
Mmh... I've experienced a love of "Attraction/love" then trying to be friends and/or lovers and failing
I think the second or third ones would probably be my favoured ones... It's a bit hard to say because I have trouble wrapping my mind around attraction and love not going together. I'm usually only attracted to people if I'm in love with them. So that love/attraction can either come first or after we're friends, but either way I wouldn't want to be in a relationship before getting to know them as friends.
As for timelines... Well the only relationship I've had that was a relationship and not about sex was with my husband. We met in May, I believe (on a forum), then we became a couple in the middle of July, and then we met in February the next year (we had sex on the first day we met in person). We were together for five years and a half altogether.
My other relationship, with my boyfriend, we met in May as well and decided to set our anniversary on the 1st of July when we realised we had no clue when we switched to being a couple. We met in the beginning of September, and that also when we first had sex (in person). And we're together right now, so that doesn't help you with the "how long does a relationship last?".
Personally I think it would also be interesting to know how long of that relationship was good. I think if you were friends first, it's likely that you'll have a harder time breaking up because you're more attached in ways other than your relationship and you're afraid of losing that too, so you might stay longer in a bad relationship. Of course I guess the opposite might happen too: you might know you'll still be friends and therefore not feel like you're losing everything, and be more willing to break up when the relationship stops working.
I do think though that it's harder breaking up when you know you're also breaking up with a friend. At least it was my experience, but to be fair I can't really compare, before that I had casual sex and one friend with benefits, in neither case was there any break up since there wasn't really anything to break up to begin with.