You bring up some great points for discussion
@jeff ..... I agree with Brickburn that some of the questions you raise are difficult to answer with a few simple statements. I could write an entire article just on my personal opinions on some of these points you raised.
In my opinion, the hunt should begin when the outfitter conceives the notion of going into business offering bow hunts. I believe it is the outfitter's responsibility to spare no effort in maximizing every possible opportunity to increase their bow hunting clients' chances for success. I also believe that the biggest factor in facilitating that concept must include that the outfitter/PHs are experienced bow hunters themselves.
So many factors must go into the equation for consistent success that it is really impossible to address them here in one short post. Every single outfitter in Africa offering bow hunts will have you set up at a water, mineral, or food source. Most will have hides pre-set to some extent. The better ones will regularly utilize trail cameras to ensure you are in the right place at the right time. In regard to serious night hunting targeting specific species, without pre-baiting sites and monitoring trail cameras you are wasting precious time.
Yet with all of these factors in place, it really does the hunter no good if the smallest of details are not considered well before any hunters enter into the bush. Being in the right spot when that dream animal walks in isn't enough if the the animal does a 180 in a cloud of dust when you go to draw because the hide you were in let in too much back light and you got picked off. Or, if the animal got your wind because the predominant sun and wind directions were not considered when the location for the hide was chosen. I could list example after example, but as a bow hunter, you get the idea of what I am saying...
During one of my last safaris, we had trail cam photos of a huge warthog coming regularly to a particular water hole. The problem was that there was that the wind was completely wrong for that hide location. Instead of chancing it, my PH and I decided to hang a ladder stand in one of the trees adjacent to the trail in that the hog was using. We put the stand up at lunch time in a perfect tree down wind with the sun setting sun on my back, and I had that giant warthog in the salt by late that afternoon. I killed a beautiful bushbuck out of a very similar scenario on another occasion. During that same safari, we also had 3 different bait sites going for me to get my brown hyena at night (which I finally did).... Would every outfitter have the knowledge and make the effort to provide these kinds of opportunities for their bow hunting clients? Of the handful of outfitters I have hunted with in Africa, only one consistently does that I am aware of, and that is why I return to them time and again. But, as you know, I am biased because I also happen to represent that outfitter here on this forum. Now, you know some more of the reasons why...
Back to your original question of "when the hunt begins?", is a pretty subjective answer depending who you ask I suppose... For me, it begins in the details long before I arrive....