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