A while back I unlocked the secret V.R. Lab (the tenth lab). I'm not sure how I unlocked it, exactly, but I noticed in the lab selection mode that there is a secret "Chrono" Lab (the ninth lab) that remains locked to me.
My question is: How do I unlock the Chrono Lab? I know it's there because I can see it when heading to the V.R. Lab.
I've finished every level in every lab before the Chrono Lab with the exception of Level 17 of the Aero Lab (the seventh lab), which I haven't unlocked yet. Does the Chrono Lab unlock after completing all the level 17s of the previous labs? If so, how do the 17th levels get unlocked? I've unlocked seven of them so far, but I'm not sure how I've done that.
Update: I recently unlocked level 17 of the Aero lab. I'm not entirely sure how I did it; I do know that it unlocked after I finished an already-completed level in the Aero lab, this time with more mercury, as well as collecting all the bonus stars.
So maybe it unlocked based on me getting enough bonus stars, or collecting enough mercury, or possibly both.
Anyway, I completed level 17 of the Aero lab, which means that I finished every level of every lab before the Chrono lab. However, the Chrono lab still remains locked to me.
So I'll ask again: Does anyone know how to unlock the Chrono lab?