I had a cunning plan to fly to a 24-hour airfield, takeoff from base just before twilight to do the 'transition from day to night' exercise, dual circuits, land, brief and solo circuits (total 3.5 hours flyong). Night stop, then take off again at sunrise -2 hours for the night navex, fly back to base and land after the end of official night (we've no lights). All seems perfectly legal, with 8 hours sleep between flights can't see the problem. Yet to achieve it, though.
TOO