This achievement is very easily obtainable on Nightmare Level 1. The 1st-4th Gaias are all fairly close together and can easily be gotten in rapid succession. This gives you 2 chances to get the achievement per attempt (Gaias 1-3 or Gaias 2-4, if it takes too long to get from 1 to 2), and even if you fail (either you aren't fast enough or you die), just start the level over again and give it another go. Took me about 6 attempts.
If you're able to get 2 consecutive Gaias within 5 seconds of each other (also very easy to do, especially with the 2nd and 3rd Gaias), you will unlock the Fast Recollecter achievement.
Here's a video showing the exact path I took for the first 4 Gaias. I would have unlocked Fast Recollector for the 2nd and 3rd Gaias as well as the 3rd and 4th Gaias, and I would've have unlocked Artificial Intelligence for both the 1st through 3rd, and the 2nd through 4th. I had already unlocked them by this point and that's why they don't pop.