Which hook to use to execute code before custom-post-type admin loads

I have a custom post-type and I would like to execute some code when entering the custom-post-admin page. I couldn’t find a useful hook so for the time being I use
add_action ('manage_mycustomposttype_posts_columns' , 'mycallback')
Of course this is not the right thing to do, especially because this hook fires too late. My callback script should be executed earlier so the script gets a chance to update the database before the posts are listed.

(I hope i make myself clear)

Does anyone know which hook to call?