On D/P..

[jnfs2014]

When did you first defeat the Elite 4?
Me:
Got the game-April 22nd.
Defeated Cynthia-April 30th.

[ThePowerOfOne]

I have no idea. I know it didn't take all that long, though.

[Macawmoses]

Oh, no clue. I got it on launch, and it was probably four or five days later.

[tibar21]

I got the game in late Februrary and beat Cynthia on March 1st.

[JrDude]

Wow... when you guys play, you play 'till you win...
I don't know right now, but it was far later then the rest of you guys (by later, I mean it took more time).

[GreatGonzales106]

I don't really remember, but it was probably a week or two after I got it (launch).

[bluaki]

I got the game on December 24 2006. My first completion of the Elite Four (and the day I got the National Dex) is marked as February 2 2007. Didn't beat the Elite Four a second time until two months later at 2007/4/9, then having the next two shortly after on 4/13 and 4/22.
It's not like I do nothing but play Pokemon Diamond when I first get it, and at that I don't try to rush through the game.

[JrDude]

Started on : 8-6-07
Hall Of Fame (1st): 9-28-07

Ok, maybe not THAT much later, but later.