In
Project Clock, projects can be assigned to users. When projects have
been assigned in this way, users can only enter hours on projects to
which they have been assigned.
To assign projects to users select Tools | Manage User Projects from the main menu. The following screen will appear:

All users will be listed in a treeview on the left. All projects will
be listed on the right. To assign projects to a user, first click the
user. Then select the desired projects and press the < button
to assign it to the user. When projects have been dropped onto a user
they will show as sub items underneath that user. To delete a
user/project assignment click the assigned project under the user and
press the - button.
Note that changes are made in real time. You cannot cancel user project assignments you have made.