Is there a way to measure a lag between unity event and it's appearence on the screen?

Hi all!

I am a PhD student at the Technological University Dublin. I am using the Meta Quest 2 to run the experiment that involves pairing the Meta Quest 2 HMD and EEG headset. The issue is that I need to know the exact time between the event happening in Unity and being detected by the LabStreamingLayer and the image changes on my Meta Quest 2 screen with high precision. Due to the specifics of the EEG signal I am working with the answer should be precise up to the millisecond. Is there some known number or should I measure it myself using photosensors, etc?

Thank you