Timeline

Over 7,000 years ago

 * Rose Quartz, Ruby, Sapphire, and Pearl are created on the Gem Homeworld.
 * Gems arrive on Earth to establish a colony.

5,750 years ago

 * Small group of rebels form and diplomats are dispatched from Homeworld to resolve the conflict.
 * Ruby and Sapphire meet
 * Garnet is formed for the first time
 * Garnet becomes a Crystal Gem

Over 5,500 years ago

 * The Rebellion begins.

Over 5,000 years ago

 * A battle occurs at the location which would later become the Strawberry Battlefield. Many Gem Warriors fall. Rose's scabbard is lost.
 * Pearl was "a few thousand years old" at the time.
 * Forced Fusion Experiments start.
 * The Pyramid Temple is constructed.
 * Homeworld Gems leave Earth.

Unknown Time Period

 * The Cluster was embedded in the Earth's core.
 * The Galaxy Warp goes inactive.
 * The Crystal Temple is constructed.
 * Ruby and Sapphire decide to stay fused as Garnet.
 * Amethyst is discovered at the Kindergarten and joins the Crystal Gems.
 * Lapis is trapped in the mirror.
 * 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 found Beach City.
 * 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, Dustylegs Jefferson, died tragically when he was hit by a train full of circus animals at a book signing in active train yard.

Recent History

 * Ocean Town is abandoned after an unspecified catastrophe.
 * Greg drops out of community college to become a professional musician and tour the country.
 * 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 is 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 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.
 * Over a decade before Year 1, Rose Quartz gives up her physical form to give birth to Steven Universe.
 * Roughly 2-4 years before Year 1, the Beach house is built.
 * Roughly 5 years before Year 1, the Aqua-Mexican restaurant goes out of business.
 * Roughly 1 year before Year 1, Connie Maheswaran and Steven see each other for the first time at the Boardwalk Parade.
 * A year before the events of "Steven and the Stevens" (And two since "Sadie's Song"), Steven performs naked at Beach-a-Palooza.
 * The summer before "Gem Glow" Sadie starts working at the "Big Donut".

1st Year

 * Dogcopter 3 premieres in February, placing the events of "Lion 2: The Movie" at some point during that month.
 * "An Indirect Kiss" occurs right before the events of "Mirror Gem" and "Ocean Gem".
 * "Ocean Gem" takes place on the first day of summer (June 21), placing 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".
 * 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. Connie is "12 and 3/4" at the time.
 * It Could've Been Great takes place several weeks after Catch and Release.

Level 2 Canon

 * Attack the Light, as well as the comics and others place at an unspecified point between "Fusion Cuisine" and "The Return", placing it in Year 1 or Year 2.

Non-Canon

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