I think any correct definition of floored must include the specific criteria that at some point the butt kisses the canvas...
How long? This is the next key question. How long do all four or the butt need to be in contact with the canvas for a legitimate 'floor'? I would contend if a boxer bounces straight back up he's not been floored. Thoughts?
Well, it shouldn't be more than 10 seconds, or else it's KTFO lol. But I agree with your take, it should be at least 3 seconds.