The Sandman's Hourglass

According to most scholars, the concept of time is something only to be pondered and never to be tested. History is littered with stories of ambitious mages who meet their end dabbling with time, often in some obscure way. In some of the higher echelons of the arcane world, discussed only as an academic curiosity, a new school of magic has been dubbed. Pertaining to the manipulation of time, Chronomancy is often considered the only truly forbidden school of magic, for the potential it has to upset the very nature of reality. Although many have attempted the forbidden art, none have ever been known to master it. Yet, there is mention of an artifact that has been imbued with the very essence of time itself. Claimed to have belonged to a deity, as no mortal could have achieved such a feat, the artifact is referred to as "The Sandman's Hourglass".
A popular folktale among the people, the Sandman is the name given to the being that ensures a good nights rest. Under this being's portfolio, however, is the guarding of time. A rare but not unique portfolio to the pantheons of Terra Mortalis. The Sandman is the common people's name for this entity, regardless of pantheon, and thus the artifact has been immortalized in this vain. 
Little is known about this legendary artifact, but theories suggest it has the power to manipulate the flow of time within a created pocket of reality - ensuring the Butterfly Effect does not cause any irreparable damage to the nature of reality. Stories around this curiosity tell of the ability to negate aging for the user, or advance it rapidly for their enemies. One such story even mentions the rather ingenious use of this artifact to advance the aging process of a dragon wyrmling, allowing the creature to reach adulthood within a mortal's lifetime. 
Stories aside, this item is generally regarded as a myth since its existence could spell disaster incomprehensible to most.