End-users didn't get to see the level names anyway, or at least not in the game.
Maybe it took just one day?
Or, more likely, he forgot that it took more days?
I tried to find something from that day in his old journals: (we don't know which year...)
https://web.archive.org/web/*/http://jo ... /1986/03/*
https://web.archive.org/web/*/http://jo ... /1987/03/*
https://web.archive.org/web/*/http://jo ... /1988/03/*
https://web.archive.org/web/*/http://jo ... /1989/03/*
But I found nothing.