In your time tracking, you have the option of adding the respective time tracking comment as a comment to the corresponding project or contact. For example, create a new time entry that is posted to a contact (in this example "sample company"), enter a comment and activate the checkbox "Add as comment", this comment then appears directly with the contact.
If you now call up this contact, the comment will appear in their master data view on the left under the area "Comments"
If time tracking comments should ALWAYS be saved directly to the contact, project or the respective opportunity, there is a chance to activate this checkbox by default. To do this, click on your user in the upper right corner of the screen and click on the field "Settings"
In the settings view, scroll to the "Time recording' and tick the available checkbox.