But the monument valley for example is right in the middle of route66 and route50. when should i do that?
I was suggesting you do that instead of the Skywalk, so basically while visiting the South rim of the Grand canyon. Many of the suggestions I made are taking you on detours from the two route numbers you wish to follow but I feel you have plenty of time to do so.

if i would drive the route66 to the end i would have a problem getting to death valley because i don't have that much time. it is going to be a lot of back and forth thing.
It's just a case of what you want to do. If you really want to drive route 66 and say you have done it from end to end, there is a 'price to pay'. I must say that I am in the 'other camp' where I would prefer to go where I want to go and not have a route number decide for me, it's whether or not you want to complete it and if the answer is no, then maybe looking at possible alternative routes is a better option. Another example is that you could complete route 66, head up to SF, through Yosemite and Death valley to Vegas and then head north to Zion and Bryce and I70/US50 from there. At the end of the day there are thousands of options on such a trip and it's for you to decide what will work best for your trip and we will give you all the help we can, so you can achieve your goal.

Enjoy the planning, it's a fun part of the adventure !!