"40 hours" in his context here is actually a work day, so 7-8hrs.

He says "40 hours" because he feels like he's managed to do 40 hours worth of work in this time, but then has to spend another "40 hours" (actually: 1 day) just going around kicking tyres.

Obviously the implication is that it's a net gain of some kind, but he's unsure if he caught everything.

(sorry to reiterate the GP, but I feel like you missed the important nuance that it's not a real 40 hours of time).

Wow, just wow. This is the first time I've encountered this particularly AI apologism. To recap:

Alice: "in the end, AI doesn't make me any faster because it still takes 80 hours to do 80 hours of work once I fix it"

Bob (AI booster): "actually you might've been holding it wrong, did you try XYZ?"

Carol (AI double-booster): "Bob, actually Alice means it took 16 hours to do 80 hours of work. So it did work for her."

Alice: "no I fucking didn't"

No the second 40 hours is a real 40 hours (two weeks), and the implication is there is no real time saving.

Sorry, my original phrasing was confusing which you should not be downvoted for. I've edited my original comment to clarify what I meant (hopefully).