Time and reality is fungible, the past and present can change and the future is but an array of ever shifting possibilities. It is woven into the fabric of the Helix and that fabric may be torn and rewoven by the Helix spiders. Magic is the means by which time and space can be transcended, but Metamagic is the structure of the Helix beyond the curtain of time and space and provides for the resoltuion of paradoxes created by temporal or alternate reality magics. As such the lower levels of metamagic have been used by some spellcasters to manipulate the nature of magic itself (Such as in extension spells).
Temporal and Alternate Reality magics can be dangerous as those meddling with such vast power should be advised. It is always good to know the overlying framework that controls such energies, the laws of Metamagic. There are laws of metamagic: The Law of Elegance: paradoxes tend to be resolved in the most simplest way possible. [Dm trying to keep it simple] A second principle is The Law of Whimsy , whereby the pardoxes are often resolved with a sense of irony, often at the expense of the individual meddling in time [Dm's displeasure] , and thirdly is The Law of Portent , where webs of destiny often serve to direct the final form of the resolution of the paradox [i.e. Dm steps in to keep things from spiraling out of control]. The fourth law, The Law of Infinite Perversity and Unintended Consequence means that there is a ripple effect to such changes that even the Gods and the most powerful Elementals of Time do not completely comprehend. [DM can always predict the outcome of things]. All the beings of the helix great and small are bound within the ultimate power of the most transcendant metamagic, the power of ultimate creation and destruction [The DM]. When travelling in time or across alternate realities, it is best to try to minimize paradoxes, meeting oneself, killing one's own grandfather, etc.