So for anyone else facing this issue in the future, here is how I solved the problem:
→ using the HTTP - Make a request module to send a POST request to Elevenlabs (instead of the default Elevenlabs module), I’m able to set the timeout to 300 seconds. This is longer than the duration of the Elevenlabs module (seems strange - if anyone from the Make.com staff sees this, please extend the duration of the Elevenlabs module to 300 sec as well 
)
→ To get the HTTP POST request module to work properly with Elevenlabs, I recommend looking at this thread: API Elevenlabs recovery mp3 files - #2 by Simo which has a useful discussion on the topic
→ In my case, I additionally had to add two “Text parser” modules. Because the JSON format for the POST request is more sensitive to breaking (due to line breaks, or unexpected " signs), compared to the native Elevenlabs integration.
My recommendation: if your text is around 1000-2000 characters, it’ll most likely be done within the time limit, and you should use the native Elevenlabs module from Make.com. If your text is longer than that, it best to use the custom HTTP POST Request. So far, nothing I encountered took more than 3 minutes on Elevenlabs btw, so a singular 300 second module, should be fine!