What you are seeing is normal behavior for
Review settings. These comments aren't made to be part of the final document, they are for collaboration and review of the document.
You can not turn off time tracking in these comments, which is an important part of the review process to provide a timeline of who made what comment.
If you are looking to add a comment that will be a permanent part of the document or does not use the review features, insert a textbox from the
Insert tab wherever you like, then edit it to add text.