So is there any compelling reason to conclude that one of these guys with a flashlight was Zimmerman with his keychain light?
I don't know about compelling, but whatever the reason W-6 indicated there were multiple flashlights, I agree with whonoze that it wasn't because Officer Smith was already there.
The first time W-6 said 'flashlights', plural, was 7:18:25.
Digressing for a moment, I'm not assuming these times are accurate to the second. There might be a delay between the connection time and the start of the recording, but I don't think it would be more than a few seconds for a 911 call. I don't think 911 callers get put on hold, absent major disaster.
Digressing within digression, I don't know that it has been established that time on hold creates a gap between Event Report connection time and recording start. That's another speculation. For all I know, connection time and recording start might match to the second, regardless of the type of call.
Returning to the 911 recordings (pop), if there is a gap between connection time and recording start, it might be similar for all the calls, and in any case it's in the same direction. Recording can't start before there is a connection. So I would expect the intervals to be at least a little more accurate than the absolute times.
Back to the timeline (pop).
W-6 said 'I think, there is flashlights' about 7:18:25, and 'There's two guys in the backyard, with flashlights,' about 7:18:41. I omitted the second one before, because I just wanted to mark the first time W-6 indicated multiple flashlights.
About 7:19:23 W-5 (Mary Cutcher) said 'Police are here.' She didn't say how she knew, and in my opinion Cutcher is the least reliable
of the witnesses. But this is the first indication of police on the scene.
About 7:19:29, W-18 said 'People are coming, I think, with another gentleman with a flashlight. I don't know if it's a policeman.' Around the time she finished saying that, she heard Zimmerman admit to the shooting, and passed that to the dispatcher about 7:19:36.
W-18 isn't a great witness either, but her real-time account is consistent with Zimmmerman's SPD interviews and Smith's report, and gives us a marker for when Smith contacted Zimmerman and began the process of taking him into custody. And that time is about a minute after the first time W-6 indicated multiple flashlights, and over half a minute after the second time.
The W-6 call ended about 7:19:04, so he would have been off the phone by the time Smith reached Zimmerman.