"on the order of 100ms"

It's misusing big-O notation for "order of magnitude", but after I initially tripped over it, it seemed clear enough.

I think they are using O(x) as a shorthand for antilog10(log10(x)±0.5).

Or, in simpler terms, O(x) = “approximately x, to one significant figure”

It’s used as a comparison to the alternative, O(1000), an order-of-magnitude improvement.