Actually for collecting the eye data I do still use an almost unaltered eye data callback function like described in https://forum.vive.com/topic/9341-vive-eye-tracking-at-120hz/ . I do still use the timestamp which comes with it as I suppose that it is an altered system timestamp.
Using Windows & Unity:
private void Update()
{
long timestamp = 0;
SRanipal_Eye_API.SRanipal_GetSystemTime(ref long timestamp)
Vector3 headPose = Camera.main.transform.rotation.eulerAngles;
timestamp = SRanipalSystemToEyeTrackerTimeStamp(long timeStamp)
}
I am proposing that the timestamp above can now be compared with eyeData.timestamp which you get through the eye data callback function for synchronizing purposes. Cheers. 😃