/ic/ - Artwork/Critique

It's fine to copy and past the structure and put more details in the next step? Or I should do always the ball and do everything from zero each step?
Asking because maybe my work will come back, so I will not have too much time to study.
I feel that I learn more drawing each ball and structure, but it takes way too many time. Do you guys impose some timer on yourselves or go free?
I deleted the sketch from the last one, because I had the feeling that was hiding my flaws.