"Sleep quantity" refers to the amount or number of hours a person sleeps. It describes how long someone sleeps during a particular period of time. Full definition
In fact, the most influential factor in your testosterone production is actually sleep quantity and quality. (t-nation.com)
This finding «challenges the predominant focus on sleep quantity in some of the public health messages,» say the authors, who argue that how well you sleep is at least as important as how much you sleep. (health.com)