In most cases of mild to medium levels of pain, hydrocollator packs can be used in intervals of 15 to 20 minutes at a time with a minimum of one to two hours of rest in between. In case of moderate to severe pain, they may be applied for longer periods of 30 to 120 minutes. This should only be done when needed. In either case, it is important to allow the body to recover and rest from the heat for a minimum of one to two hours after application.