Does the timing of IPR with Invisalign have to be exact?

IPR is basically the creation of space between teeth to allow for them to be moved into a new position. The timing of IPR is very important because Invisalgn utilizes software that simulates the movement of the teeth to fabricate each of the aligners. If a new aligner is inserted before the space that it needs has been created, then the aligner will be attempting to move teeth into a space that has not yet been created.There will be no harm done if the space is created prematurely, however it's still best to follow the instructions that have been created by their computer-generated model. I hope that you have found this information helpful,Dr. C

IPR can usually be done earlier than suggested and as the other doc said you just need to make sure you do not overreduce.  You also do not want to wait and do it later than expected since teeth are not able to move if there is collision of the teeth  

No the ipr can be done before the exact stage.  We often do it that way for patient convenience 

Your question about IPR with Invisalign being done earlier by a couple aligners is a good one.  IPRs are done to create a better fit of the teeth at the end of treatment.  This is necessary because in many cases a tooth size discrepancy, between the upper and lower teeth, can exist and the IPR helps to balance that discrepancy.  As long as the tracking of the aligners is good, the IPR can be done a little earlier or later, but the doctor has to make that decision.

Inter-proximal reduction otherwise known as IPR is  the removal of a small amount of tooth structure, much like gently reshaping a finger nail to remove a snag.  It does not hurt the tooth nor hurt your gums/smile.  IPR is often necessary to get the proper alignment, good function and best possible smile result when going through Invisalign therapy.  IPR is staged and is often done before the time it is needed or at time it is required according to the Invisalign ClinCheck model.  It should never be done later than requested as that could limit the tooth movement thus interfering with the final result.  IPR is integral to the completion of an Invisalign case when indicated.  I often ask for it to remove black triangles that might occur when the crowded lowers are straightened. 

IPR timing can be done early depending on the case.  Your treating clinician is in the best position to judge what is appropriate.  The key is not to over reduce.  All IPR could be done at the first visit in most cases, they often hold back to enhance the esthetics during treatment.