az:

Nectarines, like most stone fruit, go through a stage where they seem to just set there and do nothing. This is called pit hardening. The seed is developing but not the flesh. Then after a while the flesh starts to expand so the fruit gets larger and starts to change color. The fruit is ripe when the flesh begins to soften. That can occur as late as September for some of mine.

So be patient, you may have a late ripening variety.

Thanks for your response, Fruitnut. My main concern is that they will fry in our upcoming HOT weather. In our area, most peaches and apricots have already ripened and are almost completely gone!