All things considered it is not such a bad estimate of the time. It looks like it makes it queries the local clock three times to get an estimation of the clock deltas and network delay . Why do you think 1.8 seconds is wrong? What is your ntpq billboard?
It just seemed like it was claiming a lot of precision that, from my own experience of javascript, browsers and network latency, seemed a bit over the top. (Granted, on the order of magnitude of seconds, I'll accept that. Less than 100 ms and I grow suspicious).
