Yes, you can track time for other TimeTracker users in your org from Salesforce. 

e.g: you can track time for your Managers who do not have time to make their own time entries.

Upgrade the PK4 TimeTracker application in Salesforce to version 1.70 or above from Salesforce App Exchange

From the Multiline Time Entry tab, click the Select TT User to create Timesheet Entry button to see the list of TimeTracker users in your org. Select the user for whom you want to make the time entries. Enter the time details in the Multiline Time Entry screen and submit them.

You can enter up to 10 timesheet details at a time using the Multiline Time Entry screen. If there are more than 10 records, submit the first 10 records and then add the remaining time details in the same screen and Submit them.