TL;DR; A look to what the wearer of the Mask of Time sees, their abilities, and significant elements within the mask’s world.
This pitch originates from my origin story for Tahu, Accelerant. While it has been said that the wearer of the mask would not be able to see when using it, the question came;
“What are they seeing instead?”
So here’s a concept art of the whole scene.
I’ll break down each part;
The Timeline
The timeline is undergoing the Doppler effect; past events are in red while future events are blue. As seen in the picture, there are also many more scenes in the past, as they are events cemented in time. The future only has a few, which are events that are fated to occur, regardless of interference.
Tahu
Within the Mask of Time, Tahu’s body takes on this ethereal form; the Vahi is fused to his Hau, he has changed to a glowing gold color scheme, and has strands of time itself flowing off of him. Upon the Vahi are the elements; representing the other Toa who are aiding him in utilizing mask in the real world.
I’ve made some “rules” on how one can operate the Mask of Time at Tahu’s level.
-Holding the timeline; stops time at the current moment.
-Pulling your hand to the left slowly; resumes time to normal.
For more advanced users;
-Pull to the left quickly; accelerates time.
-Pull to the right at any speed; reverses time.
-Pulls towards oneself; erases time. It just works.
Moving on…
The Life Forces of the Great Beings
Each of these crystal structures represent one of the Three Brothers. Ekimu, Makuta, and Karzahni do not age under normal circumstances; their life energy is separate from the timeline. However, it does not mean they are immune to the powers of the Vahi. The further their crystal is from the timeline, the stronger their resistance is to the effects of time. In this case, Karzahni can withstand the effects far better than Ekimu.
Let me know what you think 
But, one more thing…
That red thing in the upper left corner.
I heard a deep saying once, from a comedy series on the YouTubes.
"It’s a funny thing about looking for answers, Tahu… sometimes you are far better off not finding them."
I t h u r t s t o l o o k a t i t.
-DarkMaestro
EDIT: Adding this idea from the discussion below;
In the picture, Tahu’s ethereal form has the Mask of Time fused to his mask. Now, he currently has no mask power when he dons the Vahi, so he can only use the time powers.
However, if Karzahni were to use the Vahi, his Mask of Alternate Futures could come into play too; the same applied to Ekimu and Makuta.
So theoretically; If the Brothers are at their fullest potential, they can do more with the Mask of Time, such as;
Causality Affirmation (Ekimu): The ability to create events that are destined to happen, regardless of timeline interference. Since this is a highly demanding task, Ekimu can only do one event per use.
Reality Overwrite (Makuta): The power to rewrite certain events within the timeline. However, it must be an event that occurs at that moment; no past or future events. While not as energy-consuming as Ekimu’s power, Makuta would need high amounts of stamina to constantly overwrite.
Alternate Reality Manipulation (Karzahni): Can control the passage of time in other realities, and possibly even enter the alternate timelines. While the Great Being’s life forces are separate from the passage of time, Karzahni cannot come into contact with the next timeline’s Karzahni; otherwise they would violently fuse and destroy each other.
These special abilities are granted only with the legendary masks. Weaker masks will have no change to the Vahi’s uses.
I’m just throwing theoretics out there; I don’t think these would ever occur in the actual story, or at any point in the lore.
