There is no single answer for how many hours a day a support belt should be worn, because it depends on your routine and what feels right. In practice, this type of belt is chosen for periods of physical strain: housework, gardening, driving, warehouse tasks, or when you return to activity after rest. Wearing it during those tasks gives you the stability exactly when you need it.
The elastic breathable fabric helps reduce heat build-up and makes longer wear under clothing more tolerable. Even so, take the belt off whenever you are sitting for long stretches in a stable position or sleeping—continuous compression is not needed during rest and can become uncomfortable. Listen to your body: loosen or remove the belt if it causes discomfort, numbness, or a feeling of pressure that seems unusual.
For cleaning, check the label on the product itself; typical support belts require gentle care, but the exact instructions depend on the version you have. A clean belt keeps skin irritation less likely, especially if you wear it often.