The story...

The final three minutes of hijacked United Flight 93 are still a mystery...

...there is a roughly three-minute gap between the time the tape goes silent — according to government-prepared transcripts — and the time that top scientists have pinpointed for the crash.

Several leading seismologists agree that Flight 93 crashed last Sept. 11 at 10:06 a.m. and five seconds, give or take just a couple of seconds. Family members... were told it stopped just after 10:03.

The FBI and other agencies refused repeated requests to explain the discrepancy.
http://www.sonoran-sunsets.com/flight93.html

Our take...

It's true that the Government say the crash occurred at 10:03, while some seismologists have quoted a time of 10:06. However, sites that pretend this discrepancy has been ignored aren't telling you the whole story. The 911 Commission did address the issue in a Chapter 1 footnote, where they explained their reasons for choosing the 10:03 time.

168. Ibid., pp. 23­27.We also reviewed a report regarding seismic observations on September 11, 2001, whose authors conclude that the impact time of United 93 was "10:06:05±5 (EDT)."Won-Young Kim and G. R. Baum, "Seismic Observations during September 11, 2001,Terrorist Attack," spring 2002 (report to the Maryland Department of Natural Resources). But the seismic data on which they based this estimate are far too weak in signal-to-noise ratio and far too speculative in terms of signal source to be used as a means of contradicting the impact time established by the very accurate combination of FDR, CVR, ATC, radar, and impact site data sets.These data sets constrain United 93's impact time to within 1 second, are airplane- and crash-site specific, and are based on time codes automatically recorded in the ATC audiotapes for the FAA centers and correlated with each data set in a process internationally accepted within the aviation accident investigation community.

Furthermore, one of the study's principal authors now concedes that "seismic data is not definitive for the impact of UA 93." Email from Won-Young Kim to the Commission,"Re: UA Flight 93," July 7, 2004; see also Won-Young Kim,"Seismic Observations for UA Flight 93 Crash near Shanksville, Pennsylvania during September 11, 2001," July 5, 2004.
http://www.faqs.org/docs/911/911Report-478.html

Is this an accurate or reasonable conclusion? We don't know, however we've yet to see any comment from dissenting seismologists that occurred after the 911 Report was released. Some will say that's because they've all been "leaned on", but you know what? It could also be because they accept this as the final verdict. Without more information, it's hard to see this claim as proving anything at all.

Update: some sites point out there’s plenty of other evidence supporting the 10:03 time; http://911research.wtc7.net/planes/analysis/flight93/ is a good example. There’s some truth in that, but it’s not quite as simple as they claim. We’ll be expanding coverage on this at a future date.