Yep. As I stated, you can falsify an event happening later than it really did by prerecording and only uploading later, but you can't fake that it happened after uploading. With clever cross-referencing, it might even be possible to prove decisively when the file was created.
Post the hash online?
Because the audio is only your half of the conversation, you could just record what would be convenient to have said before the conversation, then say something different, and just upload your prepared file.
It’s not like just because it’s in a blockchain, its content is truthful. It just confirms it followed the rules of the blockchain.