SG-1 has had several experiences with time travel. After the first Abydos mission, Carter had researched alternative applications for the stargate, including time travel. She discovered that a massive solar flare occurring at the same moment as gate travel would redirect the wormhole closer to the sun because of the flare's magnetic field, and the increased gravity would cause a slingshot effect back to Earth, sending the traveler back in time. Solar flares on the opposite side of the sun would use the sun's rotational differential to be sent forward in time instead. However, solar flares are impossible to predict, and the stargate was not seen as a viable means of time travel.
When an unexpected solar flare occurred during SG-1's mission to P2X-555, however, they were accidentally sent back in time to 1969 and were able to use the solar flare research to return home. Similar technology was used when SG-1 attempted to alter their own history after Earth joined the Aschen Confederation and humanity faced extinction. The Aschen computers were capable of predicting the solar flares which create time distortions in wormhole travel, and SG-1 was able to send a message through the stargate, back in time ten years earlier in order to change their own fate.
A device specifically intended to alter time was discovered on P4X-639, a deserted world that was once a colony of the Ancients. Faced with a cataclysm, the inhabitants had long ago created a time machine to go back and change their own history to avoid their fate, however the device never worked, and instead it created a short term continuous loop. When the device was activated, P4X-639 and 13 other worlds, including Earth, were drawn into a time loop that repeated every 6 to 10 hours.
The first evidence that the Ancients had actually mastered time travel was discovered on the planet on which Maybourne had settled as King Arkhan. An Ancient spacecraft containing a time travel device had been abandoned on the planet, and SG-1 was able to bring it back to Earth for study. Research into the area of quantum gravity suggests that time flows like rotating fluid within our galaxy, theoretically making time travel possible by allowing a traveler to journey backward and forward through streams of time at will. The Ancient device was designed to use this principle, and it manifests an energy field that encompasses the entire ship, allowing the traveler to literally fly through time. SG-1 used the device to travel back in time to Egypt in the year 3000 BC. Cautious of the Grandfather Paradox, which states that if one goes back in time and kills one's own grandfather, one's father could not be born and one's own past and the world would be changed in unimaginable ways, SG-1 attempted a mission of minimal contact and minimal impact. However, their presence in the past instead set into motion a spiral of historical events that would play out exactly the way they were meant to.
Using the technology of the Asgard, Carter discovered a way to reverse time in a localize field. When the Odyssey became trapped for more than 50 years in a time dilation bubble, Carter rerouted the power conduits of the ship to use the energy of Ori weapons fire to power the Asgard core and activate a reverse time field that essentially erased the 50 years spent inside the bubble.
Cross Reference: Ancient Time Travel Device, Time Dilation Bubble, Time Loop, Time Travel 1969, Time Travel 2010, Time Travel 3000 BC
Episode Reference: 1969, Window of Opportunity, 2010, It's Good to Be King, Moebius, Unending