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macOS and iOS's Cocoa frameworks — Core Data, Safari history, and Swift's Date type internally — count seconds since January 1, 2001, not 1970. Convert it either direction below.
Found in Core Data SQLite stores, Safari's History.db, and raw values from Swift's timeIntervalSinceReferenceDate.
The gap between this epoch and Unix time is exactly 978,307,200 seconds. Apple's own NSDate/Date API handles the conversion for you via timeIntervalSince1970, so this format usually only surfaces when you're reading a Core Data .sqlite file or a Safari history export directly, outside of any Apple framework doing the translation.
See Unix Timestamp in Swift for the API-level version of this same conversion, including why the reference date was set to 2001 in the first place.
Related
The Foundation API that produces and consumes this exact format.
A different browser, a different epoch — microseconds since 1601.
Excel, .NET ticks, GPS time, Julian day and more, all at once.