I think "day one" was an existing phrase that was confusingly extended to cover other "start of phase" concepts. Sounds like a nice way to trick your managemen

I think "day one" was an existing phrase that was confusingly extended to cover other "start of phase" concepts. Sounds like a nice way to trick your management though, "Uh no, it won't have feature X on day one, but that will be working by Day-2."