"Why is there such a diffrence in the flight times? 6h 15min one way 7h 55min the other."
Winter wind allowance, maybe different routing - plus you can pretty much guarantee there will be a straight in at NCL whereas Dubai is a lot busier and you may have to fly around the houses
Last winter I did LHR-SIN rtn - 13-10 one way 15-15 coming back................