A. The setting is purely subjective on your part as there are 12 speeds.
B. You can use the foot massager with your bare feet, with socks or even with shoes.
C. Many people like the feel of it with their shoes on. This is very helpful for people who have sores on their feet, and feel more comfortable massaging their feet with shoes on. Also, ideal in applications where the massager will be used in a public place and sanitation is a concern.
Duration: This can be used for any length of time up to 15 minutes and can be used several times a day