The value is not in spending months learning these at this stage but in getting the key under youfingers.
I completely agree with you.
I'm trying to set the way to do things easier.
I would like to start working on scales.
At the moment the four pieces im working on are in keys:
It's better to start with minors after majors are mastered.
It's better to work with C at the end of majors.
Do I start with D scale till mastered?
There's really no one and only good way to do anything and that's why you will get different answers from different people.
I don't think you can "master" a scale by just playing it. If you want to start working on scales I would recommend adding some theory study to it. I really struggled with the scales in the beginning because I didn't want to get back into the theory after 30 years break and forgetting everything, I just wanted to play. But after I gave in and worked out the basic theory, scales became easier and they started making sense to me as a system. Also I don't need to try to memorize fingerings by drilling anymore because I figured out the "why" behind them and I can work it out myself anytime.
I recommend you try to take some time frequently to think why you are doing what you are doing and whether it is working in your favor. Try to evoke some curiosity towards things so that you naturally want to figure out more about the structures you encounter in music. Use scales and other exercises to expand your knowledge and skill in a way that help you manage and understand your music better. IMO This is the key to fast and deep learning, not following any ready made formula.
So if you play pieces D, C and a minor, do play and study the scales in those keys. But don't just try to play the scales as fast and clean as you can, but think about what is the difference between them, how are they built and why the fingerings are the way they are. Study a little theory (how to build a major/minor scale and the circle of fifths) and before you know you can build and play any scale you want. The speed and fluency of fingers will come easier when your mind knows what to do. I think this will benefit you much more in the future than just practicing moving your fingers faster on the keyboard.
Children often learn to do first and understand what and why they are doing much later, but for adults I don't think this is the most efficient way because our minds already work differently. We are usually not able to stop our minds from analyzing what we do all the time, so it's best to use it in our advantage.