Flow of Time

The Flow of Time is the description of time moving from t₀ to t₁, or from one moment to it's subsequent.
Future is the potential of events occuring, and is the set of all possibilities. The sum of probabilities over all future events is 1; the median and mode of said probabilities is almost always 0; the average is almost always infinitesimally small.
Present is fickle and indeterminate time. It is time at its lease stable and most malleable.
Past is everything that already happened. It is where the flow of time has already carved its path in reality and cannot be changed.
Future turns into present, and present into past, by flowing through a timefall. The largest, most significant, and most stable timefall is Chronos's Falls. Each object and creature have their own individual timefall that forms around them.

Localization

Though time flows into all planes at the same rate, certain planes might allow or prevent less or more time to flow into them. Regardless, the perception of time is subjective: for the observer, the rate of the flow is constant, and differences in flow rate become evident only when travelling between planes. There are four types of flow rate:

Normal Flow

This is the standard rate of time, compared to the Material Plane. One hour on a plane with normal flow equals one hour on the Material Plane.

Variant Flow

On some planes, time can flow faster or slower. One may travel to another plane, spend a year there, then return to the Material Plane to find that only six seconds have elapsed; for that traveler and the items, spells, and effects working on them, that year away was entirely real.
Planes that have variant flow can be used by clever individuals to gain certain benefits; one can step into a slower time flow for the purpose of healing and regaining spells, and powerful individuals can do so in the midst of battle, return completely refreshed, even before their foes realize they were gone; certain wineries in Vintia use a pocket dimension with faster time flow to store wine and age it quickly.

Erratic Flow

Some planes have time that slows down and speeds up, so an individual may lose or gain time as he moves between the two planes. To the denizen of such a plane, time flows naturally and the shift is unnoticed. The Feywild and Shadowfell are the most noteworthy examples of planes with erratic flow.

Stagnant Flow

On these planes, time still passes, but the effects of time are diminished. Hunger, thirst, and aging might not be affected in a plane with stagnant flow. By the same token, natural healing may be affected, meaning that no wounds heal except by magic. If a plane is timeless with respect to magic, any spell cast with a noninstantaneous duration is permanent until dispelled.
The danger of timeless planes is that once one leaves such a plane for one where time flows normally, conditions such as hunger and aging do occur—sometimes retroactively. A traveler who hasn’t eaten for ten years in a timeless plane might be ravenous (though not dead), and one who has been “stuck” at age twenty for fifty years might now reach age seventy in a heartbeat.

Type

Natural