Oh yes, that could fit, possibly, but there are couple of things that don't quite make sense.   If Magnussen had made a call at that point, Sherlock was facing him and would have known.  Which would mean that for some reason, he was covering for Mary.  Again, that's possible, but it's quite complicated - it means that John has to buy the ambulance explanation (which is very dodgy in itself), and Sherlock has to set up a scenario with the paramedics so that they arrive at just the right time.   And calling the ambulance is part of the reason that John and Sherlock think they are safe with Mary - take that away, and how do they know?  Why is Sherlock so keen to eliminate the threat to Mary rather than the threat from Mary?  Why doesn't he worry about this in his mind palace?  Why doesn't he warn John?   I suppose the only explanation that makes sense in that scenario is that although Sherlock knows the ambulance story isn't true, he doesn't think Mary's a threat, but believes John will think she is without the story - so he makes it up. 

The trouble is, again, that it all hinges on the ambulance story, which is silly in itself.   You still have to believe that an ambulance would take eight minutes, and that's a fact which determines who called it.   But in reality, that isn't a fact.   The most likely explanation is actually that there were paramedics in the area when John made the call, and that eight minutes is an average (it's not as if they'd hang around outside for five minutes if they got there early!).   (In my experience, the paramedics arrive before the ambulance). 

Personally, I see Magnussen reaching for his phone, but don't see him making a call (although it's technically possible).   The post said that Sherlock couldn't have known that it took John five minutes to find him, but the obvious explanation is that he asked John - he would need to have asked John (or the paramedics or whoever) to know how quickly the ambulance got there anyway, and about other details such as Magnussen still being unconscious.

Is she talking about S3 (where we know she believes she'll lose him if her secret comes out), or about S4?  If S4, then it's very exciting!   And presumably means that we are definitely going to find out what the secret is (we're suspecting that we're going to find out more about Mary's past anyway, but still, nice to have that detail confirmed!) ... and that even the reconciliation at Christmas isn't enough for her to believe John will stay with her if he finds out the truth.   (Actually, I'm wondering if this is S3 now - I think it might be from the S3 DVD, in which case, sadly, I think she may be talking about S3 rather than S4.  I'll see if I can dig it out to check).

I think when I've called an ambulance I've just been told that it's on its way ... which is kind of ambiguous, come to think of it.    I don't think it's more of a leap of faith to believe that they just said something like that, than that we would believe that an ambulance arrives in exactly 8 minutes.   If that was the clue we were supposed to see (that John would have been told an ambulance was already dispatched), then I'd be pretty miffed.  Normally what they would do here, is keep the person calling on the line and talk them through resuscitation and emergency care until the paramedics arrive (not necessarily in an ambulance!).

I don't get the impression that he's claiming to have seen or heard an ambulance call.  It's a deduction, I think - he deduces it from the information he's got.  I think it's fairly clear in his mind palace that he hasn't heard anyone call an ambulance. 

(Not really relevant, but I thought I'd add .. in reality, the "eight minutes" is a standard - it's the time by which first responders should get to the most serious cases after dispatch.   Sometimes this will mean paramedics getting there first and an ambulance arriving later.   But they are meant to get there in less than 8 minutes in all cases.  It's not meant to be an average response time, or an expected response time (you'd hope that it was quicker if possible).   To be honest, it looks like somebody did minimal research on this and came up with the 8 minute figure, and used it for the deduction.   Which I'm happy to go along with, as it's fictional, and the characters seem to believe it, but then I wouldn't be happy to be told "You should have known Sherlock is lying because the operator would have told John that somebody else has phoned - but you still have to accept that 8 minutes!")

I should say so.
Though personally, I always believed Sherlock, anyway.

"She knows she hasn't killed him." - But she only then learns from John that Sherlock pulled through. She did not and could not know before since he was clinically dead. 

I do not see why this should not apply to S4 as well. I am convinced that in the end Mary's past and deeds will come between her and John. Burning evidence and suppressing knowledge is not a solid basis for a happy marriage. 

This has always been my thinking, too.

But then, if she thinks she has killed him (i.e. tried to kill him, and believed she'd been successful), then why would Amanda say "She knows she hasn't killed him"?  It only really makes sense if she's saying Mary didn't shoot to kill.   And there's no reason to call the ambulance if she planned on him being dead.   It looks as if she really did shoot to incapacitate, but accidentally caused a greater injury than she intended.   I know it's a little bit convoluted, but it gets even more convoluted if you go the other way (she intended to kill, but Amanda thinks she didn't, and Sherlock deduces that she didn't, wrongly because he didn't know that the ambulance operator would have told John that somebody else had phoned, etc. - it ends up going round in circles!   And I initially thought that the fact that he "died" meant she meant to kill him - but then it just doesn't piece together with the other things we're shown).

Liberty wrote:

But then, if she thinks she has killed him (i.e. tried to kill him, and believed she'd been successful), then why would Amanda say "She knows she hasn't killed him"?  It only really makes sense if she's saying Mary didn't shoot to kill.   And there's no reason to call the ambulance if she planned on him being dead.   It looks as if she really did shoot to incapacitate, but accidentally caused a greater injury than she intended.   I know it's a little bit convoluted, but it gets even more convoluted if you go the other way (she intended to kill, but Amanda thinks she didn't, and Sherlock deduces that she didn't, wrongly because he didn't know that the ambulance operator would have told John that somebody else had phoned, etc. - it ends up going round in circles!   And I initially thought that the fact that he "died" meant she meant to kill him - but then it just doesn't piece together with the other things we're shown).

Let's keep in mind that before shooting HLV, Amanda had no idea Mary was about to betray Sherlock like that. It is possible that the writers also kept her in the dark about aspects of S4.

Yes, when I looked at the original post, I thought it Amanda was talking about S4.   But in fact, she was talking about something that was resolved in S3 (John did find out her secret).   But of course, I'm expecting twists and surprises in S4.

@Besleybean, yes, I do agree that sometimes we have to take what we're being shown.  It doesn't really make sense for Sherlock not to be on Mary's side at this point, given what we've seen.  (I don't mean that you'd expect him to be on her side, but that what he does and says, what John does and says, fit with Sherlock believing Mary is OK). 

So she's a useless assassin, then?
 

Death is usually final.