Final answer:
A hand and arm massage should be performed during a microdermabrasion treatment while the mask is on the client's face, as it’s a non-disruptive time to enhance the spa experience.
Step-by-step explanation:
The best time to perform a hand and arm massage during a microdermabrasion treatment is while the mask is on the client's face. During this period, the client is in a waiting phase and the mask's active ingredients need time to work on the skin. Providing a hand and arm massage can enhance the overall spa experience, promote relaxation, and doesn't interfere with the facial treatment. It's a moment in the procedure when you have the time to pamper your client without disrupting the microdermabrasion process.