Night+and+Day+in+chapters+11+and+12-4

We think Night represents secrets.

The Dictionary says Night represents obscurity and mystery.

We think Day represents truth and honesty.

The Dictionary says Day represent ultimate reality.

In the book, during the day Hester stands on the scaffold accepting the consequences of her committing adultery. It shows the truth of what she did and she is coming to terms with it by being honest and accepting what she did. Day represents reality and truth and Hester did this when standing on the scaffold.

In the book, Dimmesdale stood on the scaffold at night and this relates to the night representing secrets. Because it was dark and no one was around, it was the only time that Dimmesdale would agree to stand on the scaffold, so that maybe it would relieve some of his guilt but still keep his secret from others.