how to add time worked to additional comments?

[Ricardo Sanche3]

Adding an additional comment should populate the Time Worked in the activity log the same way that Work Notes is tracked.

[Aoife]

https://www.servicenow.com/community/developer-forum/add-custom-field-on-activity-log/m-p/2161181 

Check out this link to see how to add fields to be tracked on the Activity Stream.  

If you are actually wanting to have the field changes tracked as a comment you will need to create a business rule that fires when the field changes and then add a script to populate current.comments = 'Time Worked ' + current.time_worked.getDisplayValue();

Aoife