You can add time details for yourself and for other TimeTracker users by using the Multiline Time Entry screen in Salesforce.
Your TimeTracker user ID should be enabled with the Check-box, "Log Timesheets for Multiple Users", only then you can enter time for other TimeTracker users in your org.
- Click here to know more about enabling the option to add time for other TimeTracker users
To enter time for other users, go to the Multiline Time Entry screen, select the user from the field "Select TT User to create Timesheet Entry", enter the time details, and click the Submit button.
Now the time details get added for the user you selected from the user list.