I suspect the latter question works better because it's softer and doesn't give as much of an out as the former. We're all busy. It's much easier to answer in the affirmative and if anything, highlighting the busy nature of your day makes it easier to say "leave me alone", but the latter is harder to answer no to, at least socially. A second or two, surely you can spare that. He's not asking for much! (Obviously, it's figuratively "a second" and more like a few minutes, but at least there's some daylight for the caller to squeeze their foot in the door.)

A lot sales pitches really prey on people's general desire not to be rude to another human being, so choosing the right phrasing to make the mark feel bad for breaking a social convention if they say no is by design.