What does it matter how long it was on screen. Anyone with enough technical skill to rip a DVD could extract all the still images and make them available online.
It matters because that’s the determination of intent. If it’s just there so quick nobody notices for over a year there probably wasn’t any intent. If they focused on it long enough for everybody to figure it out when the episode first aired there’s intent. This was the former, they used heads they had in storage, happens all the time. Yeah the Bush head was probably made by a makeup guy with rude intent, but then it wound up in a closet somewhere until some director said “I need more heads”, and there it is. I think of it like the Shatner mask in Halloween, John Carpenter wasn’t sending any message, the mask was handy and with some mods gave the look they wanted.