How to hide button "Period Structure" in Planning Book ?

Hello,

Does anyone know how I can hide the button "Period Structure" (button showing a "calendar" icon which allows to change the time bucket profile) in the planning book screen (not all of our users should be allowed to use it)? We are on SCM 5.0. Is there any user-exit, user parameter, authorization object which can be used?

Thank you.

Regards,

Klemens