knowing when a painting is done

This semester in Painting three my teacher has tried to get us to produce work very fast.  Up until two weeks ago we were making seven paintings a week.  My method to completing these painting was producing one painting every studio session and never going back into it.  Now that our class is beginning to make work for the final critique, I'm struggling with going back into the painting that I perceive as finished.  I think the seven paintings a week was a good assignment in getting us to make a lot of work in s small window of time.  However this assignment has inhibited my ability to  know when a painting is done and how to add to paintings.  For the rest of the semester I am going to try to work on adding to my paintings and not completing them in one sitting.  

Pictures of work I have made in one sitting.  You decide if and how I should add to them.