Capstone projects are broken up into a series of milestones. The milestones have an initial due date and a final due date. They are there to allow for an iterative development cycle.
The initial due date is the date when I will first check your progress for that milestone, if you have submitted work for it. I will then provide you with feedback which you will then address and re-submit. The process will continue until we reach the final due date by which point I will give you a final grade for the milestone. The feedback will mostly be in the form of new Issues, associated with the milestone, in your github project.