We can setup TimeSheet to track only the time without having to selection Activities by denying them the Permission.
– Identify the permission assigned to the user from Edit User screen.
– Click on Administration Icon at the top to select Permission under User/Department from the left Pane.
– Click the Permission to edit.
– Expand TimeSheet to uncheck 'Show Activities in TimeSheet' and Select 'Activity Selection is not required' from the drop down list.
– Click 'Save' to apply changes.