What length of time should I schedule my massage session?

This will depend on what your goals are for the session.  If you are just looking for one targeted spot that is giving you grief, such as your neck and shoulders, or if you have chronic pain in one shoulder, then a 30 minute session should be sufficient.
However, I would recommend you start with an hour.  Often the spot that is giving you grief is more than just in that spot.  It's usually one area that causes a kinetic chain reaction of events.  Thus, having a full body massage at the first appointment will help the massage therapist assess other issues that my be contributing to your pain, and suggest frequency and length of appointments from there.

Fascia is a fascinating piece of the pain puzzle in the human body.  It, quite literally, runs through every muscle, organ, and adipose tissue connecting everything together.  Women who have had one or more c-sections, tend to have more low back pain in their daily lives.  This is due to how a c-section is performed - cutting through 7 layers, including muscle and fascia.  After healing time, this area can be strengthened to help support the skeletal system, and thus helping ease low back pain.  Massage can also aid in easing chronic pain.  If you are lucky enough to have a visceral massage therapist nearby, you may want to set up an appointment to see how they can help.

Another item to consider is your pocketbook.  You may benefit from shorter sessions more frequently, as opposed to longer sessions further apart.  But this will be a choice you need to make.  A good therapist will present what they believe is the best course of action, and then let you make the decision.

The bottom line is that a massage therapist does not "fix" people.  We are merely facilitating the body into its own healing.  With all the education and years of experience I have accumulated in my career, I still find surprises in client tissues and muscles, that don't follow the "norm". Every body is different and every body heals in various ways.