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It should instantly acquire your location as the time it takes for the simulator to pass on the GPS co-ordinates to the simulated device should be instant.
If this doesn't work, you need to re-sync the GPS on the simulated device. Instructions can be found within this gallery here.
As you can see in this screenshot, I have already checked into London Heathrow Terminal 5, which in this case was a false check in.
Please read the disclaimer! You can find this and more, including the explanation - as well as the pro's and con's of using spoofed geolocation on the ZDNet iGeneration blog.