According to this MSE post the 5 minute grace period has not gone anywhere, but there is more than just the 5 minute timer that determines if an edit is rolled into the previous revision or a new one created.
According to this answer from Shog9:
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 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
This behavior was implemented in March 2015.