Sleep restriction is a commonly used, non-pharmacologic method of treating insomnia and what you're doing with sleep restriction is taking away a time that a person is lying awake in bed.
For example, if they're laying in bed for eight hours but sleeping only six hours, you're trying to take away those two hours that they're lying awake in bed. So you start to decrease their time in bed to six hours. What that essentially does is it creates a little bit of sleep deprivation which in the long run will help them get a deeper sleep and a more consolidated sleep.
Now, when they're sleeping about 85 percent of the time for those six hours, you start to increase their time in bed by 15 minute increments. There is no set schedule or rate that this is done. It depends on how the patient is doing.
So in the long run this will help consolidate their sleep and get a better quality sleep rather than lying awake in bed for eight hours trying to get the sleep that they might not be able to obtain.