The product is made with a moisture-wicking technical fabric, which helps draw dampness away from the skin and reduces the feeling of overheating under clothing. That makes it more practical to wear during normal daily activities, such as moving around the house or going about light tasks, than a non-breathable band would be.
There is no standard rule that applies to everyone, because how long the belt should stay on depends on the reason it was recommended and on your own comfort. Some people wear it mainly when they are active and take it off during rest; others prefer a looser fit while sitting or lying down. The key is to use the Velcro adjustment to change the pressure as needed during the day.
If you are considering wearing the belt while sleeping, check with your doctor or physiotherapist first. Sleeping positions can shift the belt, and overnight compression is not automatically appropriate for everyone. During the day, check the skin under the belt from time to time, especially in warm weather, and take short breaks if the area feels irritated. If your specialist has given you a specific wearing schedule, follow that schedule rather than relying on comfort alone.