If you need to track time not related to your work items, you can use the General Tasks feature. General tasks can be: If you need to track time not related to your project, you can use the General Tasks feature. Note that only users with the Server Administrator permission can manage non-project general tasks.
When you delete the task it will no longer be available for logging time but old time entries against this task will remain unchanged.Time Tracking Settings
General Tasks
Managing non-project tasks
Creating Non-project General Tasks
Renaming Non-project General Tasks
Deleting Non-project General Tasks