The Time Jumper is a Puddle Jumper capable of time travel. It was built, or at least reconfigured, by a Lantean scientist named Janus, to make use of a device he invented and installed in the cargo hold. In the main timeline, this experimental, although entirely successful, technology was banned by the Lantean Council in order to prevent dangers associated with time travel. (SGA: "Before I Sleep")
In an alternate timeline, members of the Atlantis expedition discovered a special Puddle Jumper in Atlantis's Jumper bay, one which was capable of time travel. In that reality, the expedition had suffered tragedy immediately upon arriving at the Ancient city, because the shield had begun to fail from lack of power, causing the city to flood. Desperate and with no method of escape, the alternate versions of Major John Sheppard, Dr. Elizabeth Weir, and Dr. Radek Zelenka sealed themselves in this Jumper as the Jumper bay flooded. They subsequently activated the time device by accident.
They traveled 10,000 years into the past, arriving at the final days of the Ancients' war with the Wraith. Orbiting Wraith ships sieging Atlantis mistook the newly arrived Time Jumper for a contemporary Lantean craft, and opened fire, causing the Jumper to crash land on Lantea. The alternate Sheppard and Zelenka were both killed in the crash, but the alternate Weir and the Jumper itself were rescued by the Ancients inhabiting Atlantis, including Janus. Meeting a woman from 10,000 years in the future prompted the Lantean Council's decision to ban further time travel research, thus changing the timeline such that Janus's prototype would no longer be left behind for the expedition to later find. Fortunately, Janus ensured that the expedition would also be saved from drowning, in the new timeline. (SGA: "Before I Sleep")
An identically-equipped Puddle Jumper, equally capable of time travel, was later discovered by SG-1 abandoned on a planet in the Milky Way galaxy. This newly discovered ship's time travel device was visually and functionally identical to the Janus prototype, implying that in the new timeline Janus chose to disobey the Lantean Council's ban on time travel research. (SG1: "It's Good to Be King")
This Jumper was later used by SG-1 as a means of traveling back in time to ancient Egypt, in order to steal a Zero Point Module from Ra. After SG-1 were killed by Ra with the exception of Dr. Daniel Jackson, who survived in ancient Egypt, the alternate SG-1 from the future traveled back in time using the same jumper found in Egypt, to restore the timeline that the original SG-1 had altered in the past. (SG1: "Moebius, Part 1", "Moebius, Part 2")
The Time Jumper was used by Major General Jack O'Neill and Vala Mal Doran to travel back in time to rescue SG-1 after a solar flare left them trapped in the past, simultaneously taking a detour to rescue a crashed Asgard. During the adventure, Loki destroyed the time machine part of the Jumper and trapped SG-1 in an alternate 1947 created when Lieutenant Colonel Cameron Mitchell and Vala Mal Doran were stuck in 1908 during the adventure. After stopping an attack on Earth by Ra and Qetesh, SG-1 used another time travel device to return to 1908 to rescue Mitchell and Vala and then return to their own time. Also during the adventure, the Time Jumper collided with a Goa'uld Ha'tak in 1908, destroying it and causing the Tunguska Impact and preventing a Goa'uld attack on Earth. (Stargate SG-1: Roswell)
The Time Jumper was stolen by three rogue Tok'ra in 2008 to undertake a mission to try to save their species by convincing Egeria to spawn more Tok'ra. They kidnapped Doctor Carolyn Lam who had the Ancient Technology Activation gene to pilot it, but SG-1 followed them through time to 2492 BC using the Solar observation outpost on Praxyon, eventually recovering the Jumper and after driving away Ra, using it to return to the present. (Stargate SG-1: Moebius Squared)