It looks like the resolution of the
notificationInterval and of the
position is only about 0.5 secs. If that's the case, you won't be able to set notificationInterval to less than 0.5 secs; even if you could the position would only be accurate to within 0.5 secs. You can set it to something larger, but still with about 0.5 secs of resolution.
I don't think it was intended to be used to display a timecode label to within a fraction of a second. Position notifications have typically been used to trigger saving bookmark information, which doesn't need that level of accuracy.
You can use a Timer node to trigger more frequent updates, doing "fake" timecode updates that you sync up with the position every half second or so.
https://github.com/belltown/