The initial fireball of a nuke is caused by xrays absorbed by air and develops in microseconds. Basically all at once, since the xrays move at the speed of light. A spherical region of air just ionizes.

The expanding fireball moves quite a bit slower and increases 10s of meters (from an initial ~10-100 m) over several milliseconds[1]. After that it slows down even more, and if you measure every millisecond you'll see the fireball expanding by meters.

[1]: https://pbs.twimg.com/media/Dbf8IK9V0AA38po.jpg

A DEQNA ethernet controller card can measure to an accuracy of 100ns which is around 20m at the speed of light. Shockwave velocities in the ground are in the order of 1000 to 10000 m/s or 1 to 10 m/ms so sampling at 1ms intervals should be precise enough.

In fact here is a graph produced by CORRTEX https://digital.library.unt.edu/ark:/67531/metadc1200655/m1/... which shows a velocity of ~3 m/ms or 3000 m/s. The sepcialised equipment has much better resolution and samples much faster than every millisecond.