Within Teamwork, you can set start and end dates for individual projects on your site.
Open the Overview section of your project and go to the Dates section of the project details sidebar on the left.
If you don't yet have project dates set, you will see an option to Set Start & End Dates.
You can choose specific start and end dates for the project. If there are tasks already populated in your project, the dates will default to take those tasks' dates into account. You can override these defaults to set specific ones.
You can also choose to ignore conflicting task and milestone dates or mark the project as complete.
Once you have added project dates, you will see them listed in the project details pane. You can also edit the dates directly from here either by clicking one of the dates or via the Edit option (visible on hover).
For more information, see: Adding a Project