Some brain tumor resections are performed with patient awake and responsive to questions. This is to assure maximum resection of the tumor without effecting surrounding functional brain tissue. The patient may be asked to move extremities or report numbness if the surgeon is approaching normal brain tissue. This way he or she can remove as much of the tumor as possible.
Occasionally a patient may not tolerate this or may need to be put on general anesthesia in the middle of the procedure. In those situations the surgeon has be very cautious and may only be able to do a sub-total resection of the mass.
The answer to your question is that the duration of the surgery is very much multi-factorial and unpredictable.
There may be other contributing factors that could reduce the length of time brain surgery lasts. If the patient leads an otherwise unhealthy lifestyle, for example, as a habitual smoker or drinker, the patient's life expectancy would naturally be reduced by many years. His brain surgery, as a result, would not last very long either.
Contrarily, the younger the patient is, the longer their brain surgery should last. Infant patients who have undergone brain surgery have the potential to live for decades. The longest surviving patient to have undergone brain surgery as an infant is now 102 years old. As the patient is now experiencing dementia, we can say with confidence that his brain surgery lasted almost as long, roughly 101 years.
Good luck to your friend.