Application on starup

Hy u’all
Im looking for a way to start an application (SBClient) at user logon but before the desktop, or explorer.exe loads. The idea is for the users to enter data on the application before they are allowed to continue working on Windows. I could write a script that stops explorer.exe, loads the application but, how can the script know when the user is finished entering data. The application runs with explorer.exe stopped.

This would make my bosses year.
Thanks