I just answered a question and edited it within a short period. But this is what I saw:
What happened to the grace period of 5 minutes for editing a post?
The comment broke the grace period.
According to ex-CM Shog9's answer,
Edits will be rolled into the previous revision if the previous revision was created by the same author and none of the following conditions are present:
- The previous revision was created 5 minutes or more in the past
- A comment has been added to the post after the previous revision by anyone other than the editor
- An answer has been added to the post after the previous revision (even if the answer was posted by the editor)
- The previous revision was a rollback
- The new revision is a rollback
- [as of April 3rd, 2017] The question was closed after the previous revision.
According to the post's timeline: