It's programed in the protocol.. and he waited for others to download the network before the first block was mined from my understanding
Discussion
AFAIK there isn't any time measures in the code. There is only block height and difficulty adjustment algorithm.
Maybe nostr:npub1n9czx2x9grvfzlhaaxsa6hu57psvs0nvfx88w92ds64a2h6k5cmqtktcar knows the answer?