Of course you can move on lol. You can do whatever you want! But I do think they look good enough that you don't to spend as much time on them.
I think one important thing to notice is that you spent a little over a week just practicing the head shape. I would go through each facial one week at a time and do a lot of studies from images and practice the basic constructions. While you're doing this try to keep practicing basic shapes and forms.