Warm up time for record playing

rvpiano, Of course the improvement is palpable. Why would the microphone changing it's sensitivity and frequency response be any different then your system doing that. I know for an absolute fact your hearing does this. Read any book on the physiology of hearing. Your ears and brain are far more flexible than your Hi Fi. People just do not understand how their senses can be so affected by the environment.  There is nothing about us that is static. 
Walk into a very bright room from a dim one (movie theater) and you will start squinting. Eventually things settle down and you won't have to squint...because your pupils have stopped down and limited the amount of light that enters your eyes. Guess what!  Your ears work the same way.

Chakster, it takes one to know one. 

mijostyn,

What you say could be a possible explanation.

I don’t think so. I don’t doubt what mijo states about the physiology of it all and it probably is a factor...... to a degree. However, wouldn’t the same physiological “break in” occur when listening to live acoustic music?  In live settings I don’t experience anything close to what rv describes. noromance mentions a couple of possibilities. I would add the possibility that your particular cartridge does indeed “relax” during the first half hour or so. Maybe.

I am in the camp of a little of this and a little of that is probably closer to the truth than having to pick just one. Enjoy the music