As far as I know, he didn't. He called the chained block structure a Timestamp Server in the white paper. Then people came up with Blockchain, which got sullied by shitcoiners, so Bitcoiners rebranded to Timechain and attributed it to Satoshi somehow. https://i.nostr.build/YgLJe.jpg
In the v0.1.0 source code Hal Finney sent to mrb on bitcointalk (@zorinaq on twttr), Satoshi does reference the timechain. Also numerous references to the timechain in pre-release notes (supposedly from Satoshi sent to ppl who requested them in Nov 2008) posted by Cryddit on bitcointalk, but since I can’t verify those I won’t post them here yet. https://i.nostr.build/oMOAv.jpg https://i.nostr.build/zdJ93.jpg