Focus on an object or feature in sight.  As the caster concentrates, their left eye begins to witness time in reverse, seeing further and further into the past.  Simultaneously, their right eye begins to see time progress at an accelerated rate, seeing further and further into the (currently-most statistically-probable) future.  Through their left eye, they might see burnt paper unburn, and become readable, then as time continued back, watch the words "unwrite" themselves off the page, leaving a blank parchment.  They might see people or creatures pass through a space in reverse.  Through their right eye, they might see an unused new journal begin to form words on its pages as they "write themselves" in, then after some time, get torn, or scribbled over, or fade.  This might allow the caster to view the combination of a currently-secured lock at some time when it was (or will be) solved and open.  They might also attempt to read a lost spell scroll, or examine a destroyed piece of evidence.  Maybe determine what someone else is planning based on what they write, or how an object will be primed in the future, and then prepare against that outcome beforehand.

Area of Effect:
Typically, this spell is cast and then the caster spends all of their attention on the focused-upon object or area.  However, the caster may wish to look around at their surroundings with anachronistic vision, or even walk about and observe the area as it once was or likely someday will be.  This requires a Wisdom saving throw of DC 15.  Failure means the caster becomes disoriented with a sense of vertigo, and must cease movement and focus solely on the original target of the spell in order to avoid losing concentration.  They cannot attempt to look around at their surroundings again until the spell is cast anew.

Rate of Change and Control of Flow:
For the entire round spent actually casting the spell, the caster sees the past/next 24 hours (4 hours per second).  They may change or pause the perceived flow of time by performing a Wisdom save, as though 0 rounds have passed so far.  After this first round has passed, the caster may change the rate of the vision once per round.

Rates are:
> > > > Stopped,
> > > One second per round,
> > One minute per round,
> One hour per round,
One day per round (DEFAULT),
> One week per round,
> > One month per round,
> > > One year per round,
> > > > One decade per round,
> > > > > One century per round

Each attempt to change this rate may only shift over a number of rate categories equal to or less than the caster's Wisdom modifier.  Each change in rate prompts an immediate Wisdom check of
[ DC (9 - 1 per every 2 caster levels) + (number of rounds spent concentrating so far) + (number of rate categories attempting to change this round) ]

So for example, shifting from days/round to full-stop is a difference of 4 rates.  If the caster is Level 3 and was concentrating for 6 rounds at this point, then the DC is (9 - (level 3 / 2)) + 6 rounds + 4 rate = DC 18.  Shifting from centuries/round to full-stop after concentrating for a minute would be (9 - (level 3 / 2)) + 10 rounds + 9 rate = DC 27.  A level 20 caster would attempt the same shift as (9 - (level 20 / 2)) + 10 rounds + 9 rate = DC 18.  Shifting one rate category per round prompts more checks, but each check will have a lower DC to contend with, and may be necessary for lower-level casters who wish ultimately to shift across many rate categories.

Failing this Wisdom save causes the caster to immediately suffer a debilitating migraine for 1d20 minutes (Disadvantage to all Int and Wis skills and saves).  This also immediately ends the spell, unless the caster chooses to suffer one level of exhaustion.  No rate shift can be attempted while the caster is suffering a migraine, and additional castings of this spell automatically fail until the migraine clears.

Observing only events of either only the past or only the future exclusively requires the caster to cover or close the opposite eye.  Casters missing one or both eyes, or otherwise blinded, can actually still see out of the appropriate eye socket(s) for the duration of this spell, and still need to go through the same physical motions to block one side or the other.

The material components of this spell are a piece of red glass and a piece of blue glass, each of which are held up to the caster's eyes.