Timeline

Over 6,000 years ago

 * Ruby, Sapphire, Pearl, and Bismuth are created on the Gem Homeworld or one of its colonies.
 * Pink Diamond and her Gems arrive on Earth to begin a new colony.
 * Centipeetle and her crew members travel to Earth in the Ancient Gem Colony Ship.
 * Rose Quartz and many other Gems are created in the Kindergarten.

Over 5,750 years ago

 * Rose and Pearl defect from Homeworld and form the Crystal Gems.
 * Pearl was "a few thousand-years old" at the time.
 * Blue Diamond arrives on Earth. She establishes her court and oversees the removal of the then-forming Rebellion.
 * Sapphire is sent to Earth along with three Ruby guards, including the one soon to become Garnet. Sapphire gives Blue Diamond her prediction of the rebelling Gems.
 * The Crystal Gems' direct attack on Blue Diamond occurs.
 * Garnet is formed for the first time.
 * Garnet becomes a Crystal Gem.
 * Ruby and Sapphire decide to stay fused as Garnet based on advice from Rose.

Around 5,500 years ago

 * The Rebellion officially begins.

Over 5,300 years ago

 * Lapis Lazuli is caught mid-war and is poofed during battle, and then collected by a Homeworld warrior, mistaken to be part of the Rebellion forces and put in a mirror for information to be given by her.

Over 5,000 years ago

 * The Beta Kindergarten is established mid-way through the Rebellion in haste to create more troops.
 * Jasper is created among these troops.
 * Pink Diamond is shattered by Rose.
 * A battle occurs at the location which would later become the Strawberry Battlefield. Many Gem Warriors fall. Rose's scabbard is lost.
 * Bismuth was bubbled by Rose, and left in Lion's pocket dimension.
 * Forced Fusion Experiments start.
 * The Cluster was embedded in the Earth's core at some point in these experiments.
 * The Pyramid Temple is constructed.

Around 4,500 years ago

 * Homeworld Gems leave Earth.
 * Lapis Lazuli's mirror is abandoned at the Galaxy Warp and her gemstone is trampled over and cracked during the evacuation.
 * A flash of light is set off by the Diamonds, corrupting Gems caught in it, including some Homeworld Gems. The only known surviving Gems are Rose Quartz, Pearl, Garnet, Bismuth, and Lapis Lazuli.

Unknown Time Period

 * The Galaxy Warp goes inactive.
 * Amethyst emerges and is later discovered by the remaining Crystal Gems.
 * Pearl finds Lapis Lazuli's mirror at the Galaxy Warp.
 * The Crystal Gems construct the Crystal Temple.
 * Homeworld's resources become limited as Era 2 of gem production begins.
 * Peridot is created on Homeworld.

19th century

 * "Nearly 200 years ago", Captain William Dewey and his crew are attacked by a gem monster and rescued by an unknown fusion gem. Dewey goes on to establish Beach City.
 * Buddy Buddwick begins his career as an author.
 * In the summer of 1862, William Buford Buchanan, Beach City's most notorious arsonist, sets a record of 335 fires. He drowns after diving into the ocean trying to evade police.

20th century

 * In 1965, the author of the No Home Boys series, Dustylegs Jefferson, died after being hit by a train at a book signing event in an active train yard.
 * Ocean Town is abandoned after an unspecified catastrophe.
 * Greg drops out of community college to become a professional musician and tour the country. He changes his surname from DeMayo to Universe.
 * Greg records Space Train to the Cosmos.
 * Roughly two decades before Year 1, Greg falls in love with Rose Quartz and decides to stay in Beach City. He was 22 at the time.
 * Several months later, Greg records a music video with the Crystal Gems, learns about fusion and unsuccessfully attempts to fuse with Rose Quartz.
 * Greg begins working at It's a Wash, becoming its owner some time in the future.
 * Greg starts growing a beard and records "Let Me Drive My Van (into Your Heart)".
 * Over a decade before Year 1, Rose Quartz records a video for Steven.

21st century

 * 12 years before Year 1, Rose Quartz gives up her physical form to give birth to Steven Universe.
 * Roughly 5 years before Year 1, the restaurant Aqua-Mexican goes out of business.
 * Over 4 years before Year 1, construction begins on the Beach House.
 * Two summers before Year 1, Sadie starts working at the Big Donut as a summer job.
 * Roughly 1 year before Year 1, Connie Maheswaran and Steven see each other for the first time at the Boardwalk Parade.
 * Roughly 1 year before Year 1, Steven performs in his underwear (or possibly naked) at Beach-a-Palooza.

1st Year

 * Dogcopter 3 premieres in February, placing the events of "Lion 2: The Movie" at some point during that month or in early March.
 * "An Indirect Kiss" occurs right before the events of "Mirror Gem" and "Ocean Gem".
 * "Mirror Gem" takes place on the first day of summer vacation, which is June 25. That places the events in the first half of season 1, including Beach-a-Palooza, from "Steven and the Stevens", in spring.
 * "Horror Club" appears to have taken place on or around Halloween.
 * "Winter Forecast" takes place during December.
 * "Maximum Capacity" takes place around Beach City's annual New Year's fireworks, marking the end of the year.

2nd Year

 * "Marble Madness" takes place in early spring. The first spring buds can be seen on the trees around the Maheswarans' townhouse.
 * "Open Book", "Story for Steven" and "Shirt Club" take place before "The Return" and "Jail Break".
 * "Full Disclosure" takes place right after the events of "Jail Break".
 * "Joy Ride" takes place a few months after the events of "Fusion Cuisine".
 * Peridot is found during "Keeping it Together", a while after the events of "Full Disclosure".
 * In "Onion Friend", there's a schedule showing when Yellowtail will be home. Based on the crossed out dates on the chart, making it take place at some point in June, before Yellowtail's expected return on the 25th.
 * "Nightmare Hospital" occurs almost a year after the events of "An Indirect Kiss", in the summer, as mentioned by Connie.
 * "Sadie's Song" occurs roughly a year after "Steven and the Stevens", since Beach-a-Palooza is an annual event.
 * "Back to the Barn" starts right after the end of "When It Rains".
 * "Too Far" starts 3 days after "Back to the Barn".
 * "The Answer" and "Steven's Birthday" take place on Steven's 14th birthday, on August 15th. Connie is "12 and 3/4" at the time.
 * "It Could've Been Great" takes place several weeks after "Catch and Release".
 * "Message Received" appears to start in the early morning after "It Could've Been Great", and "Log Date 7 15 2" appears to start during the daytime, soon after "Message Received".
 * The flashback portions of "Log Date 7 15 2" span several weeks.
 * Peridot makes her 7 11 2 entry immediately after Steven gives her the voice recorder, placing it before the beginning of "Too Far".
 * In her 7 12 2 entry, Peridot mentions that it's been 30 Earth days since she was captured in Catch and Release.
 * She makes an undated log entry after watching a "Camp Pining Hearts" tape for 78 hours.
 * The 7 14 2 entry takes place after Opal lifts up the nearly completed drill, placing it during the same timeframe as It Could've Been Great, between the end of the Peace and Love on the Planet Earth montage and the scene where everyone shows Steven the completed drill.
 * She makes the 7 15 2 entry at the start of the episode, and describes the events in "Message Received" as having just happened.
 * Fall is arriving in "Same Old World", as stated by Steven.

Level 2 Canon

 * Attack the Light, as well as the comics take place at an unspecified point between "Fusion Cuisine" and "The Return", placing it in Year 1 or Year 2.
 * The main portion of Too Cool for School takes place in June of Year 2.

Non-Canon

 * "Say Uncle" is set before "Story for Steven". Garnet still has her pre-regeneration outfit.