As a timestamp on the current situation as of March 2019. I've looked back at different comments and it varies across the last couple of years.

Either there is some inconsistency or maybe it has changed from when swordie did it in Dec to when I did it in Jan - I'm coming up to 9 weeks and waiting. As of yesterday, KF has directly told me it's 'approximately' 6-8 weeks for Elite Silver to be confirmed. What they can't explain is why it's taking longer than 8 weeks.

Not easy trying to plan 3 flights with SQ when I live in Europe and it needs to be within 4 months but you may be waiting more than 2+ months for Elite Silver to be confirmed. My wife did the same and she is at 6 weeks and waiting. We are both on the same flights so my hope for her Elite Silver to be approved beforehand is even more slim.

For anyone doing this in the future, I would wait until Elite Silver is confirmed before booking the 3 flights but then like swordie's situation - be aware you might have to book the 3 flights very quickly if they approve it in a few hours. Even though I have given myself a 3.5 month window from registering to flying it may not work with either me or my wife obtaining Elite Gold.

I'm half joking and I doubt SQ would be that calculative but the cynic in me thinks that given KF can see I have flights booked in April that Elite Silver will be approved just after the first flight in effect forcing me to book another flight within that 4 month period to qualify By approving Elite Silver within 5 hours for swordie when they see no flights booked also adds to that cynicism. I doubt there are hundreds of people doing this status match and the usual efficiency is not on show here.