Other forms: quiescences
If there's a particular time of day when your ten kittens settle down to nap, you can call that their period of quiescence, or the time when they are all quiet and restful.
The noun quiescence looks similar to the word "quiet" for a good reason: quiescence is a quiet spell or state. It's used often to mean "dormancy," or the quieting of a symptom or a disease, such as the quiescence of a child's asthma symptoms during the winter months. The Latin root word is quies, which means "rest or quiet."