As Al E. correctly mentions, a new feature (implemented in March 2015) creates a new revision rather than rolling it into the previous edit when any one of several specific conditions are met:
- The previous revision was created 5 minutes or more in the past
- A comment has been added to the post since the previous revision by anyone other than the editor.
- An answer has been added to the post since the previous revision
- The previous revision was a rollback
- The new revision is a rollback
(Source: Reset question grace period once an answer has been posted)
But you seem to dispute that these conditions exist:
None of those conditions are true for this question though
However, you are incorrect.
For the answer in question, the timestamp on your edit is 20:42:25Z. The timestamp on Tim's comment was 20:42:22Z. So while you may have started editing before Tim's comment, his comment beat your edit by 3 seconds. Once that comment was left, your grace period ended immediately.
And for this question, you have the same exact situation. Your first edit was committed on 20:46:25Z. Tim's first comment was at 20:46:24Z, beating your edit by a second. So again, the grace period ended as soon as Tim left his comment and your edit created a new revision.