The appropriate usage time of massage devices for people with specific health conditions varies greatly depending on the type of condition, the body part being massaged, and the intensity of thehand massager machine. Here are some general guidelines:

• Neck and shoulder pain: For those with mild neck - shoulder muscle strain, 15 - 20 minutes of use per session, 1 - 2 times a day, may help relieve muscle tension. However, if it is a more serious cervical spondylosis, especially with nerve - root compression, the time should be shorter, about 10 - 15 minutes each time, and the frequency should be adjusted according to the doctor's advice.
• Lower back pain: In cases of simple lumbar muscle strain, 20 - 30 minutes of massage per time, once a day, can promote blood circulation and relieve pain. But for patients with lumbar disc herniation, overly long - term or high - intensity massage may exacerbate the condition. They may need to limit the use time to 10 - 15 minutes per time under the guidance of a doctor.
• Joint problems: For people with osteoarthritis in the knee or hip joints, 10 - 15 minutes of gentle massage around the joint area per time, 1 - 2 times a day, can be beneficial. But for patients with acute joint inflammation, using a massage device is generally not recommended.

It is crucial to note that before using ashiatsu neck and back massager with heat, people with specific health conditions should consult a doctor or a professional physiotherapist. They can provide personalized advice based on the specific situation to avoid potential harm caused by improper use. If you can tell me more details about the specific health conditions, such as the type of disease, the affected body part, and the severity, I can give more targeted suggestions.