For any curious, here's how I figured one achievement every 18.5 minutes: (d=days, hr=hours, min=minutes, ach=achievements, the rest is simple math)
1010 ach in 13 days
1010 ach/13d
1010 ach/312hr
3.237179487179487179487179487 ach/hr
0.05395299145299145299145299145 ach/min
0.05395299145299145299145299145^-1=18.534653465346533 min/ach
And by the way, here's the text of the achievement so the wikilinks work:

Null and Void
Use a Mothership to trap a Nullifier in a Vortex.

Unfortunately, they recently changed Vortex to where it does huge damage to a single target, so this achievement is based on old info.
http://www.sc2pod.com/trackers/blue/sta ... 2/?id=1132

Cavez wrote:Mothership moves slowly, can teleport to any Protoss building, can do huge damage to a single target with Vortex and cloaks everything nearby on the ground (including buildings). Mothership is build-limit-one. This is done primarily for balance reasons. You use her as a base defense that can be anywhere you want in a flash. Sometimes you push into an enemy base with her. Testing on her remains a pain because she is so high-tech we don't see her in a lot of games. Right now she is reasonably cool, but we are not in love with her yet.

That's a lot of achievements

Though I have no way to prove it, I created that achievement!
Then again, who else but the true creator of the achievement would actually bother to try and claim credit? Especially now that it's already outdated, apparently! Curse you developers for ruining my awesome puns!
I guess if there's still a Vortex-kinda animation it still sort of works.

I checked the logs and your ip address matches the one that created that achievement, so it's confirmed
Added your signature to it, hit ctrl+f5 to see it.

Wow, grats Roatigas!

That's cool.

Nice work! Keep them coming!

Check out my Achievements, too