That's all true, as far as it goes, but are there not considerations other than energy consumption?. One suspects that such a long cycle may result from the water being at a temperature too low to kill most bugs and maybe too low to clean 'properly'.If it does result in lower energy consumption, and you can kick it off when you go to bed or go to work, then it might as well take 5 hours as 5 minutes.
Kind Regards, John