Nellisir
Hero
Yeah, not so much. I didn't have any trouble finding sources.So you are wrong
"an object, event, or character in a film or story that serves to set and keep the plot in motion despite usually lacking intrinsic importance" (Merriam-Webster)
"in film, a plot device that has no specific meaning or purpose other than to advance the story; any situation that motivates the action of a film either artificially or substantively. " (Urban Dictionary)
"An object or device in a movie or a book that serves merely as a trigger for the plot." (Dictionary.com, which was actually linked from Oxfords English Dictionary)
Lucas was using MacGuffin correctly; a macguffin is the motivating factor in a story.
A sonic screwdriver could be considered a macguffin; it's an anything device that moves the plot forward, but it's really more of a magic wand than a macguffin.
In all cases a macguffin advances the plot. It's the goal, not the enemy.
There are stories in which the time-lock could become the MacGuffin, but generally it's not.
Anyways, your argument is with the dictionaries of the english-speaking world, not me. Have a great day.