I needed to #include "nrf_delay.h" instead of #include "nrf.h".
I measured 1.25 us high time and 1.75 us low time with my scope. Not great given the clock rate should be 64 MHz with a clock cycle period of 15.625 ns... but also not absolutely terrible for my needs.
Given the terrible inaccuracies of Arduino's micros and delayMicroseconds methods on the nrf52 boards, hopefully others find this much better delay method helpful!