Fair question. I went through an extensive period where I asked myself this question daily.
In short - spirit guides will always provide you information that assists in your soul's development. It will always be uplifting and make you feel loved and empowered. If any of the information you received makes you feel fearful, belittled, or less than, it was your ego talking to you.
Most sessions are about 90 minutes. The first 15-30 minutes are consultative to assess your goals or issues, then you lay fully clothed on a massage table while we work with your energy field. The last 15-20 minutes involve assessing what we learned during session and next steps to further your healing process.
This answer varies from individual to individual and depends on the issue. Many people report that one session can resolve what years of psychotherapy were unable to resolve. Most clients are able to clear the core issues within 3 sessions - spaced several weeks apart. However a deep-set physical illness will likely require more work, because healing happens on the emotional/spiritual level and takes time to affect the physical.
I recommend scheduling them 1-2 weeks apart to allow time for internal shifts to take place.