As a few people have pointed out your boyfriend is stuck in the middle here, if he wants the money then he is going to have to be "on call" between the hours stated. If he thinks it is too much he can tell the company, however don't expect many fares, if any, to come his way.
Although not directly employed by the company, they still have a "duty of care" to ensure your boyfriend isn't over doing things. You will probably find wording to the effect in his contract, with the company stating it is the drivers responsibility to ensure he is fully rested and informs the company if he feels to tired to carry out a tasking. This puts all the responsibility onto your boyfriend to ensure he is in a fit state to operate the vehicle when called upon to do so. By accepting the fare he is saying that he is fit and able to do the task, therefore any accident would be down to your boyfriends decision to drive not the companies.
It may seem a bit harsh but that is how companies operate to protect themselves from prosecution.
It is a drivers responsibility to ensure they are fit and healthy to get behind the wheel of any type of vehicle even if the boss of the company tells them to do so, every one has the right to say no but most say yes to keep their job.