Hi,
The Advanced Installer license is
per-developer (not per-system). This means that your company requires an Advanced Installer license for each developer (user) which uses Advanced Installer.
For example, if two different developers (users) use Advanced Installer to build installation packages, you need two different licenses (one for each developer).
Therefore, to answer to your question, you need to have a different license for each developer (user) which uses Advanced Installer, even if only one developer (user) uses the build machine at any given time.
You can read more about the Advanced Installer license here:
http://www.advancedinstaller.com/licenses.html
Regards,
Cosmin