"The Hourglass (Steven and the Stevens)" is a magical object that used in "Steven and the Stevens." In the episode it is stated that they had been looking for it for a thousand years. It has different atributes and history in the "Pilot" (see "The Hourglass (Pilot)"); this is due to the Pilot not being canon.
The Hourglass allows the user to time travel. The Pilot provides more information on the limitations the Hourglass has, but since it is not canon these limitations might not apply to the Hourglass in "Steven and the Stevens."
In the Pilot, it takes the owner back to a specific time in the past, but only for the same purpose the owner chose to use it. From the moment it activates, only the individual who initially uses it is able to use its power. Steven's initial purpose is to improve his comeback in arguments, so he could only time travel to instants where someone insulted him. In the actual show, there seems to be no limits to what it may do: Steven goes back in time to warn his dad about impending accidents, to form a band, and to run away from and chase after someone.
Steven and the Stevens Edit
The Hourglass makes a second appearance (First ignoring the Pilot) in the episode "Steven and the Stevens." It is kept inside the Sea Shrine which only appears once every 100 years after an hourglass is taken. Despite Amethyst taking the wrong hourglass and triggering a flood intended to empty the spire, Steven manages to collect the real Hourglass and is safely warped back to the Crystal Temple with the Gems. After unintentionally wishing, he stopped his dad from allowing Yellowtail to back his boat into the car wash. Steven then discovers that the Hourglass is capable of sending him back in time. However, he soon wishes that he was able to prevent himself from stopping his dad after the trunk, hauling the boat, crashes into an electric pole, lighting the car wash on fire, which results in his dad losing his business. Now realizing that he can make a band for Beach-a-Palooza, Steven recruits two other past Stevens to form a band and perform the song, "Steven and the Stevens". However, when the present Steven tries to set up personality roles for each Steven (making himself the handsome one), things go wrong as they reject his authority. The three past Stevens begin singing some wild rock music, kick the original Steven out of the band, and hire Amethyst as the drummer much to Steven's annoyance.
After realizing that he needs to prevent himself from ever creating a band of his past selves, he goes back in time to before he made his first wish, managing to stop himself. However, the three other Stevens are able to track him down. After this, present Steven and the other three Stevens go through time, battling each other during the events of "Gem Glow", "Rose's Room", and "Ocean Gem". However, by the time present Steven goes back to the moment he first takes the hourglass, there are many Steven clones already fighting. Present Steven convinces the clones to stop fighting, before destroying the hourglass. He tells the Steven of this timeline that he will have to do something else for Beach-a-Palooza before vanishing from existence, erasing most of the events of the episode.