I think the 10:18 time is close enough that it doesn't matter much -- I think it was sometime between the two collapses, which is the important point. My initial estimate of 10:20 to 10:50 was based on a guess about the angle of the shadow of the fireman on the sidewalk, but I don't consider that to be anything but a ballpark. This new YouTruth video uses a different video from an HBO special, which includes a few seconds earlier shot looking at the shadow of the restaurant's canopy on the wall. There isn't any detail about how that analysis was done, but 10:18 seems to be in pretty good agreement with the fireman's watch.
I've listened to that sound track several dozen time now, and I'm still not sure what the fireman says, but it really doesn't sound like "seven's exploding." My best guess is "something's exploding" or perhaps "stuff is exploding." Anyway, it doesn't seem likely that from two blocks away with tall buildings and a lot of dust and smoke between them, anyone on that street could positively identify the sound as coming from WTC7.
I saw a comment on one board by someone who claimed that an engineer friend had noticed that the audio was in mono when the people were speaking but the explosion sound was in stereo. I've downloaded several versions, but the only ones I've found so far are either mono audio tracks, or stereo with identical audio on both tracks, including the explosion section. Looking at the wave profiles, there appears to be some evidence of an analog limiter in action throughout the track -- no real clipping where the waves are chopped off flatly at the top, but some apparent rounding -- but I can't see any real difference in the explosion section. The highest peaks are about the same level throughout. Spectrum analysis shows the same range of frequencies throughout -- just more low frequencies during the explosion (which might be expected) -- so that doesn't seem to indicate tampering.
It seems strange that the original version with some credible provenance hasn't turned up, but I'm willing to accept that the explosion sound might be genuine. The "truther" problems remain, of course, that A) that video doesn't really identify the source, and we know lots of stuff was exploding after the first collapse spread a lot of fire; and B) this was about 7 hours before WTC7 fell, so "controlled demolition cutter charges" doesn't seem like a very good guess.