agree, I think unless you're just playing the same record over and over again - which no-one does - there's no real way to assess it just by listening.
I'd suggest they 'burn in' purely because people expect them to as they read it somewhere. I've never noticed it myself, they've all sounded fine right from the off.
If there was something to change in the first few hours I'd suggest it could only be the suspension compliance. Whether that would be audible I don't know. Maybe. But I doubt it would be noticeable just with casual listening to lots of different records.