I actually don't find this to be unreasonably precise. I saw a video that showed how the blast was captured on around a dozen independent devices (smartphones,

I actually don't find this to be unreasonably precise. I saw a video that showed how the blast was captured on around a dozen independent devices (smartphones, surveillance cameras) and how that data could be used to reconstruct a very good 3D capture of the blast and resulting smoke cloud. If the FBI spent X hours of simulation time to reproduce the 3D results captured on those videos, they might get it down to that precision (and who knows, maybe they just ran a lot of renders and 552 was the one that looked most right, while anything between 538 and 564 was also fine).