I think sometimes this is put in the rules just to stop someone taking the plane to say Dunkeswell from Bournemouth (for example) and having 2 weeks there and then flying back. In the meantime no one else has been able to use the aeroplane. I assume the billing would be 2 hrs per day more than 3 days? So for a 7 day trip you'd have to fly 8 hrs which is reasonable for a flying holiday? In MHE of the group I was in, this rule was never enforced, the only one that was enforced was that if you hadn't used all your hours by the end of the year, then tough, you lost them!
Also the group I was in before allowed everyone to take a 2 week holiday but you could not have more than one booking like this in the diary at any one time.
Also if it is a last minute thing and the diary is empty, one could just book the aeroplane and take it away....