It's more or less up to you as the user, but there are 2 options.

  1. Create a general project "Departure" and when the employee is going to or from a project, they can use this option.

             *The disadvantage is that it's difficult to assign a project to the arrival and departure times this way (ie: a note)

        2. They create an entry/exit activity and assign it to relevant projects.

             *This way the assignment is automatically recorded