Hi guys, I've unlocked this today after e-mailing wordament as I was number one in the 'daily' leaderboard but no achievement.
The response I got was that not only do you need to be top 250, but also have at least 10,000 points and played 100 games. I had met all requirements except for the 100 games. I played a few more and reached 100 and the achievement unlocked at the next 'rolling reset'
So just to confirm to everyone that yes, you can do it on the daily leaderboard but just being top 250 won't suffice, you need the 10,000 points and minimum 100 games. Similar to how originally you needed a set number of points or games as well as being top 250.
Hope this helps you all guys and good luck!
You're a star! Cheers matey! That'll be what I did wrong too lol. Good to see a few familiar names during games too, almost like spotting celebrities :P