Cazatou,
Time and time again in my Air Force career I have started a multi stage task knowing it could not be completed within a normal crew duty day. So have you, and most others on this thread no doubt.
The only point of importance here, is that at the time of impact and at his planned landing time at Inverness, he would have been within his crew duty limits.
Once at Inverness, whether he planned to break crew duty, ask for an extension or a night stop, are matters of pure conjecture. Therefore they have no relevance to the crash