Duration between laser hair removal sessions? I’m having a full body laser hair removal treatment.

Because laser hair removal needs to be timed for when the hair is in its active growth phase, typically the sessions are spaced a set amount of time apart throughout your series of treatments. Sometimes early sessions are spaced 4 weeks apart, and later sessions 6 weeks. If you're not comfortable with your technician's suggestion, you should ask them for more information to better understand the reasoning behind their recommendation.

Different body parts have different anagen( active) phases. During the initial few Tx's, it is important to catch them in their growth cycle-every 4 wks for face, 6 weeks for body. After a few sessions. its ok to extend the time between treatments by a couple of weeks

The laser hair removal usually is scheduled around the follicles cycles.  Typically the first few sessions are 4 weeks apart and then the later sessions are scheduled 6 weeks apart.  Depending the equipment used the number of sessions may vary. The newer technology like Xeo by Cutera typically needs 6 treatments. 3 of them 4 weeks apart and then 3 of them 6 weeks apart. 

For laser hair removal the spacing has to do with what the growth cycle is for that area.  For hair removal on the face spacing should be 4-6 weeks, body 6-8 weeks and legs 8-10 weeks. I would space your treatments if doing all in one sitting every 8 weeks.  If you are splitting into two sessions or body/arms and legs follow the above ranges.  Hope that helps with your treatments.

The suggested treatment wait time between sessions is ideally 6 weeks. Years ago, the thought was to follow the human telogen phase (sleep/rest phase) which is longer than that in human hair in most body areas (therefore treatment times were recommended to be longer, sometimes 12-16 weeks).  Newer thinking following more studies in recent years has proven that enough hairs are still active at 6 weeks and in mammalian hair, there is enough melanin active even in the telogen phase to shorten the treatment times to 6 weeks.  Occasionally in my practice, after we have done several treatments (4-6) and the hair is really thinning and reducing in number, we may extend the treatment time to 8 weeks, but that is rare.  I would not say I agree with simply extending it by two weeks with each successive session from the start.  However, every physician or laser technician should reevaluate your progress from time to time to ensure your are accomplishing 
your desired outcome.  Hope that helps.  

The length of time in between treatments will vary based on what part of the body is treated.  The laser can only "see" and treat the hair when it is in the active growth phase.  For the face, hair cycles turn over about every 4-6 weeks so that is when you would have your next treatement done.  Basically what you're waiting for is that next group of hair to go in to the growth phase so that it too can be treated. 
For the arms and torso we schedule every 6-8 weeks, while the legs are scheduled every 8-10 weeks.  For best results, I would stick to those time frames to be sure you're getting the most out of each laser session.