In general, 60 minutes is an appropriate length to receive a relaxing, full body massage. It allows a few minutes for each area of the body. But in 60 minutes, it is unlikely I can address an area in pain and perform a full body massage. With clients who have a particular area of pain or discomfort (such as low back or neck issues), I typically focus on that area and do as much of the rest of the body as time allows in a 60 minute massage.
And I want to point out that scheduling a 30 minute massage does not mean that your therapist will perform a full body massage fast. I find it virtually impossible to provide a full body massage in less than 45 minutes, and even that is pretty fast with no time for extra attention to tight areas.
How often you get massage is also a factor in the length of your massage. If you get massage infrequently, you might consider a longer massage to ensure the therapist has time to address any tight or painful areas and attend to the full body. Initially, it may take 90 minutes to perform a full body massage on a client with numerous aches and pains. But with regular massage and appropriate self-care, the time required decreases. Or, if a client has a particular injury or chronic pain condition, we might decide that a 30 minute massage once a week that focuses on their troublespot is the best plan for them.
In closing, I will just point out that numerous clients have told me that they wish their massage had lasted longer. No one has ever said they wished their massage was shorter!