i think the best way to examine this is to collect more data points, i.e., see what your travel-time looks like for other events and see how consistent (or not) the computed velocities of the waves for each are. a single event could be an anomoly.
as for timing, the units will always be within one sample of time to actual real time (on the condition that the NTP daemon is connected to a good time source). for the original 1D, then, this is 20 milli-seconds (50Hz sample rate), while for all other units 10 milli-seconds (100Hz sample rate).
also take into consideration that seismic wave velocities are extremely variable depending on soil structure. and the location of the event too, in reference to yours (is the source located below you? or totally horizontal to you? of course, probably some mixture of both…) can also have an influence on this.
(for your example, the event is very close to directly beneath you. in this case, the wave will be travelling mostly up, most likely through bedrock, which will be very fast. as opposed to a quake far away, which will spend more time at the surface before it reaches you, where the soil is softer and slower.)
i’m curious to see what a collection of results will look like. and, try to pick some events that are farther away and see what kinds of numbers that produces.
p.s. while i’ve picked some stuff up along the way, i’m not a seismologist, so please take all of this with some salt in hand… any real seismologist out there who sees an egregious error in my post, please correct me…