You should most definitely change your juice after one track day....if you drive a Nascar sedan or nitro dragster.
I've track raced with Porsche and Alfa Romeo clubs since the 80's, and I think that few of the raceheads I've known change their oil every event, or even every second or third event. Your car is stock, and your lube is a good semi-synthetic. Patman is certainly correct in that a UOA will answer your questions, but personally, I wouldn't change that oil any more often than 2,000-2,500 miles or so, even with several track events, for a stock street car. Just one faux beer snob's opinion...