The timer function shows up in the top right of the task bar if you have the correct user permissions set.
By default the account holder will have access to both the time tracker and time tracker admin. Time tracker admin allows the user to add and edit time entries for themselves and other users.
Default Roles and their permissions:
Project Manager role: Access to time tracking admin
Interior Designer: Time Tracker
General Contract: Time Tracker
Here is a quick video on how to edit user permissions for the timer and time tracking admin.