AI in 360 and editing closed captions

You could go to the Media Library (View tab -> Media Library) of a blank Storyline project, import your audio from whatever tool created the text to speech, and with AI Assistant, all of those files would have cc's automatically generated for them. You don't even have to use the files on any slides, just import them into the Media Library and AI Assistant will automatically generate them. You can always edit the captions from there, and even export them back out of Storyline if you need to!

In this screenshot, the button in the upper right imports audio files. You should be prompted to have captions generated automatically, and Storyline will want you to review them, or you can edit them. The same "Edit captions" dropdown also has an "export" option if you need the captions back outside of Storyline.