Hi @vwgx3, I can confirm that the timestamp is accurate to within a few ms for this purpose.
It corresponds to the point in time when the image has been read from the image sensor. Whilst there is some variability according to camera specific settings the specifics of this are not public domain for the Tobii Tech range of Eye Trackers. We do not output corrections for this potential variability for Tech trackers, however it is mainly the same point in time but up to a few ms in variability.
Tobii Pro trackers are designed and documented for use cases where lower variability and extensively documented timing values are available.
So ultimately, yes, you can depend that the timestamp received is on you can judge is accurate to the moment at which the gaze is taken especially for interaction purposes.
Regarding licencing, I am waiting to hear back, but hopefully this information is of some use to you.