With a mega session of 4000-5000 taking anywhere from 8-10 hours how long can the donor hair be exposed before it starts to die? I have heard 6 hours? Can anyone SHED some light?

Currently, there is a great deal of research in this area. After the donor strip is harvested, it and the grafts which are dissected from it are placed in what is called a “holding solution”. This medium can be as simple as normal saline, or it can be made up of a number of ingredients whose purpose is to maintain the health of this living tissue. The addition of glucose, amino acids (which make up proteins), and other “growth factors” are being studied in relation to graft survival while out of the body.
While certainly not common practice, I am aware of an incident wherein an exceptionally large case was actually carried over to the next day, the grafts being stored overnight!!
Those grafts had about a 75% survival rate when transplanted the following morning!!
In general however, our experience has been that even in large cases (4000 or more grafts), survival rates are not significantly affected even after 8-10 hours following removal and before placement. That being said, in general in most practice situations, grafts are not held prior to placement any longer than 6 hours at the most.
Good question.