Two Minute Rift Achievement Exploit
So I recently figured out a way to bypass the actual need to do it in two minutes. Here are the steps below.
Requires two people minimum, 5 extra rift fragments.
1. Start a rift with your two man party. Complete it up to the Rift Guardian boss. Tell player who is not getting achievement to wait.
2. Leave the game, and leave the party. Start your own game. With blackjack. And hookers.
3. Open up a rift in your own game. Immediately leave.
4. Join the other person's game, complete Rift Guardian boss.
5. Hand in the quest immediately to ensure you get your two minute achievement.
This is achieved through use of the fact Blizzard decided to start the timer as soon as you created a rift, not when the rift you're in was created.