The Kanohi Vahi was foretold to exist years before it's own creation to the point where the Brotherhood of Makuta created a creature who existed SOLELY to find it.
One might speculate that it was foretold via the power of the vahi sending a vision of itself into the Past... yet by your own admission that should be impossible since the Vahi has absolutely no control or power pertaining to going BACK in time. And if it was an idea of the Great Beings, how come NONE of them ever showed any interest in a Temporal Artifact?
Question #1 HOW did this prophecy of the Vahi come to be?
Furthermore, apparently Makuta Teridax wanted the vahi so he could "use the Vahi to speed up the process of erasing the Metru Nui Matoran's memory with the Matoran Pod." Yet this purpose is rendered entirely null and void when its revealed that the Matoran Spheres did their job as the Matoran's memories were all erased and remained that way for 1,000 years until the Turaga told them what their origins even were! Clearly all teridax needed to do was put the captured Matoran in pods and wait for a few days -a month at most! This does not at all fit in with the persona of the scheming, manipulative, PATIENT Teridax we all know so well; it just doesn't make any sense that he'd be so impatient over something so... frivolous and trivial.
Question #2 What did Teridax ACTUALLY want the Vahi for?
Why would anyone even introduce a relic that is supposed to have control over Time if A) the only time-related powers are 'Pause' and MAYBE 'Fast Forward' when the mask ISN'T cracked, and B) it has ABSOLUTELY NO relevance to the overall story?! Its pointless the only time its ever relevant and then its never relevant again! It doesn't even do anything cool!
Question #3 [and this one goes out to the WONDERFULLY 'creative' TTV cast] Why even have a Mask of Time at all, if nothing is done with it, and you have no intention of doing anything with it? [And to TTV: Why not have the island LITERALLY frozen in ICE and then set up tension agaisnt the Ice people later on for that precious civil war you guys want so much? Food4Thought]
UPDATE: Then again, maybe TTV DID decide to scrap the Brickonicle Vahi altogether in favor of literal Ice, and I just stopped listening to the podcasts months ago, so I wouldn't have known that. But they seemed to really be in love with that idea, so I doubt it