Its general because I have no real answer for you, it will depend very strictly on the athlete. Some athletes that do multiple events may compete more often than others that only do 1 or 2, just because you can't always get quality work in all your events in the same track meet. Plus, some athletes can handle more competition better than others. It is a very individual determination.
I know I was being general, but it really does depend on the athlete and the time of season.