Glossary
Mac absolute time
Seconds since 2001-01-01 00:00:00 UTC, the epoch used by LSQuarantineTimeStamp. Add 978307200 to convert it to Unix time.
Mac absolute time counts seconds since 2001-01-01 00:00:00 UTC. LSQuarantineTimeStamp in QuarantineEventsV2 uses it. Adding 978307200 gives Unix time, which is what datetime(LSQuarantineTimeStamp + 978307200, 'unixepoch') does in sqlite3.
The column is declared REAL, but SQLite may store an integral REAL value as an integer on disk, a documented storage optimisation, so a parser must accept both encodings. Do not confuse this epoch with the time field of the quarantine attribute: that one is hexadecimal Unix seconds and converts with date -u -r $((16#66f7c2a1)). Mixing the two shifts a timeline by 31 years. See QuarantineEventsV2 forensics.