Contractors like to talk, and exaggerate.
Today my broth set off a fire alarm, so I calculated the clearance of the kitchen, with the adjacent bathroom fan. I figured that the fan would clear both kitchen and bath in 14 hours, based on it being a standard 100 CFM fan, with the room capacity being 1400 cubic feet.
Then I learned I could remove the cupboards, stove, fridge, but that would still be 1000 cubic feet, meaning it would take 10 hours.
I think he meant to say it would take the powder room which is 240 square feet, would take 20 minutes. Unless that fan is a superfan(and it should be based on how much I paid for the renovation), the guy was just talking out of his behind.