This, like many other things with Curves, which are franchises, depends on the location. Both Curves I’ve been a member of have offered showers and changing areas.
The hours, too, are set by individual owners. My first Curves was 7:00 - 7:30 (though they closed for a couple of hours in the afternoon when they first opened), and the one I’m at now is 6:00 - 9:00.