Agree wouldnt put hours on it. Would just put proficiency/ accuracy as the concept. He could get it down in 4 weeks or it could take him longer. To me it may be coming out as not something to enjoy but another chore (From his perspective). Just go out and hang with him and the bulls-eye is the goal. Could even make it interesting offer a $5 for every one he makes.This would give you the time to access whether he is using proper form. If he is using proper form it would help you guide him better on why he isnt making the shot. Is the bow too much for starting to learn the mechanics? Do you test it to make sure it is sighted properly for him.
For me i had an issue shooting my grandfathers rifle growing up. Wasnt nothing to do with the gun after all a gun is a gun. The stock was too long for me, the eye relief wasnt ideal for me it put me too far from the scope, along with the focus since he wore glasses. But having the same build and eyesight as my father we could swap rifles and guns no issue and shoot each others.