The phrase "sleep clock" refers to the body's natural rhythm or schedule for sleeping and waking up. It is like a built-in alarm clock that helps regulate when we feel tired and when we feel awake. Full definition
This toddler sleep clock helps her fall asleep faster and stay asleep. (thenaptimereviewer.com)
Your baby's internal sleep clock helps put her to sleep at a certain hour, and helps wake her up at pretty much the same time each morning. (sleepconsultantprogram.com)
Regular to - bed and wake times keep biological sleep clocks on track and make it easier to avoid sleep troubles. (entrepreneur.com)