Janeway tried that in an early episode of Voyager, and Torres said, "no, when I said two hours I meant it. I don't exaggerate", and Janeway accepted it. A rare really cool Voyager moment.In Sci-Fi or tech heavy shows, regarding ship repairs/computer reboots/system hacking etc.
When the General/Captain/Commander/Boss says: "How long will it take?" to which his underlying replies: "At least 2 hours, sir".
Only to have the Boss say "You've got 10 minutes!"