I think I would sit down (with him) and list his day from beginning to end as a list of tasks he has to do and time when he has a bit of free time choice (I am all about the visual aids).
Then for everything I would make notes about that task....is it optional or mandatory? Does it interfere with other people in the family? Does it have to be done that way.
My young kids had to eat breakfast and brush teeth in pjs. It was the rule and the reason behind it was they only had x number of school clothes and the breakfast and toothpaste always ended up all over them.
So I came up with that order...once they could manage to eat 99% of the time spill free and brush teeth without major toothpaste mess, they dictated they order.
I would then go through the list and ask...what would make brushing teeth less of a problem for you? My older son does better with a spin tooth brush and toothpaste he picks out...all about a bit of control with strong willed kids...not that they can get out of doing it but that they have input and their opinion is listened to.
We can't budge here (you can't have an hour in the bathroom)...but here is what we can do.
Let's try these changes for a week and comeback together...you take notes on your copy of the schedule/plan and I'll make notes and then (when he want to whine you can tell him to "make a note of that" for the meeting.
Controlled choices and control....not running the show, but feeling autonomy and listened to.
