Hello CncTuba,
The first thing you'll want to do is isolate where the problem is coming from. Try connecting the headphones you have to a different device. (another computer, a tablet, smartphone, etc.) then test out the audio and see if the same thing happens after 20 minutes.
If the issue occurs with a different device then you'll know the headphones are the source of the problem. If it does not occur with another device, then you'll know the computer is the source of the problem.
If you isolate it to the computer, then here's some steps you can use to determine if anything is interfering with the Bluetooth connection: Resolve Wi-Fi and Bluetooth issues caused by wireless interference
You'll also want to make sure you've covered the basics like restarting the computer and making sure it's up to date.
Shut down or restart your Mac
Update macOS on Mac
Cheers!