If you’re following this book as a course, you will be submitting assignments through GitHub Classroom. This is actually pretty straightforward — as long as you have been committing your changes regularly and pushing them to GitHub, as soon as you’ve pushed the last change that is necessary to complete the assignment, you can consider it submitted. There is no extra “submit” step.
The penalty for late work is clearly stated in the syllabus. GitHub tracks your commits by day and time, so we will treat the last commit date/time as the submission date/time. If this is after the due date, then the late penalty will be applied accordingly.
For this reason, be sure that you do not make any commits after the due date, unless you are actually still working on the assignment, and accept the late penalty.
Extensions are at the discretion of the instructor. If you have a valid reason for needing an extension, please contact the instructor (not the TA) as early as possible. If you are granted an extension, you will be given a new due date, and you will be expected to submit your work by that date. However, you do not need to request an extension if you are simply submitting your work late, and expect a late penalty.