Shorten the duration of a series of files

Hello, I am an audiobook narrator and a client wants a book shortened (i.e., sped up). There are about 90 separate audio files. Their total length is about 12 hours. How can I shorten the entire audio to make the book about 10.5 hours? Any help, greatly appreciated. And I realize this is probably an easy thing to do. I'm still learning! - Chris