They should have a badge just for the first one to get to 50. I don't know what to name it but it should be unique.
If the badge is unique, it will not reward the best or even the fastest player. It will end up rewarding the player with the best ability to game the system to achieve that goal, and it will definitely be rewarded before first sunrise after the game goes live.
Never underestimate badge hunters. I wouldn't be surprised if a badge hunter hacked their way to that badge ten minutes after the game went live.
If I wasn't so busy, I wouldn't be surprised if that badge hunter was me. There's a reason the badge-hunter.com site was originally called "Badge Whores." I was still acquiring a few last really hard to get badges a month before shutdown on characters that were about to disappear into the aether (Triumph managed to achieve its first, and I believe only, Really Hard Way Magisterium on October 28th, just 33 days before shutdown).
Don't dangle raw meat in front of badgers, is what I'm trying to say.