Prepopulate Note Field
Prepopulate Note field option is located on the
Templates configuration page in Time Tracker (templates.php).

Prepopulate Note field option in Time Tracker
When selected, it automatically puts a first found template body from the
Template dropdown into the Note field on time entry pages. This accelerates data entry by eliminating a step to select a template.
Consider a situation when you have multiple projects, each one having only one associated template, and the
Bind templates with projects is in effect. In this case the Template dropdown will only have one entry. When using
Prepopulate Note field, the corresponding template body auto-fills the Note field upon project change.

Note auto-fills upon project change in Time Tracker
What happens when multiple templates are associated with a project? A
first found template body from the
Template dropdown is used.
The
Prepopulate Note field works independently of the
Bind templates with projects option. Without project binds, we see all defined templates in the dropdown, and the first one from there is used.

First found template body auto-fills note without project selection
Time Tracker User Guide