The Amulet of Time is a small pendant that holds a portion of the Sands of Time.
Unlike the Dagger of Time, the Amulet of Time holds no real special qualities or means of protection for its wearer. Instead, it is used primarily as a backup for the wielder of the Dagger of Time.
It holds a portion of the Sands of Time within its hollow and shaped like a miniature version of the Dagger's hilt. The Sands contained inside appear to be just enough to refill the Dagger of Time if in case the sands in the dagger runs out.
Events of The Sands of Time
When she is captured and later escapes with Dastan (who has been framed for the death of his adoptive father by his uncle), she attempts to steal the Dagger of Time, Dastan discovers that the medallion holds sands and so he stole it away from her.