I cannot imagine a continuous procedure that takes 36 hours to complete. What exactly are they cutting for such a long time?

If this is about making extremely delicate incisions in the brain of the patient or something like that, I cannot imagine that a surgeon who has been working for 35 hours and probably was already sleep-deprived when they started will do the best possible job.

Just seems very likely to me that handing over to a rested person after 12 hours or so, when some kind of milestone has been reached, would lead to better results for everyone involved.