Within Teamwork.com, you connect your Harvest
    account to your projects to track time.
To log time to Harvest, you will
    first need
    to enable the
    Harvest integration on your Teamwork.com site via
    the site
        settings. 
Once enabled at site level, you can enable
    Harvest for individual projects. Go to
    the Settings area of a
    project and
    select
    the Integrations subsection.

In the section for Harvest Time Tracking,
    toggle on the switch on the right to enable
    the integration.

Once you
        toggle on the Harvest integration, you can
        choose from two time tracking configuration
        options:
- No, only use Harvest
 - Yes, allow both Harvest &
        Teamwork
 

For more information, see: Logging Time to
        Harvest