Videomaker – Learn video production and editing, camera reviews › Forums › Cameras and Camcorders › Professional Camcorders › Canon XA20-25 › Matt – according to page 89
"When you are monitoring the audio, you can choose to synchronize the audio signal with the video signal or monitor the audio in real time. Use the [Monitor Delay] setting to select the method. Note that there will be a slight delay when you monitor in real time. Regardless of the setting, however, the audio and video signals recorded will be synchronized."
I have this same feature on my Panasonic GH3. It allows you to hear either what the camera is "hearing" (delayed) – or what the camera has already recorded (no delay).
This can be useful in determining whether the source of an audio issue is external or internal to the camera, but I never use it – it's too distracting.
What amazes me is that Canon Tech Support clearly hadn't read the manual! I hope you didn't have to pay for that call 🙂
Hope this is helpful,