According to their website they have a race on November 19, 2011. They say the races start at 12:30pm, but not sure how many there will be.
In the summer they had races run every 35 minutes or so until 1:00am. You can read more details about summer program and it may give you a clue on the winter program and the atmosphere in general.
You can find more information about the Mijas Racecourse if you cut and paste this link into your browser: