Transition is the passage from one state, stage, subject, or place to another : change
b : a movement, development, or evolution from one form, stage, or style to another.

But also the word transition is used in musical modulation
b : a musical passage leading from one section of a piece to another…

An abrupt change in energy state or level (as of an atomic nucleus or a molecule) usually accompanied by loss or gain of a single quantum of energy

The psychological time frame of transitions are always marked by the human act of responding and being affected by psychological changes, intervals of Revolutions, out bursts of Riots etc.