I like to search all posts (not topics !) that been made in the last 24h. The search mask doesn't allow me to do this because I have to enter a search string and cannot leave the fields blank or enter wildcards.

Under active topics you can only search and display the topics, not the posts. I have in my old Ubb6.5 such a feature to search the posts like this:

This was put in my ubbt_registerednav.tmpl and give my a one click overview of the actions in the last 24h. I miss it.

ok, this seems to included in V7.2x