A 6502 takes 7 cycles to execute the reset vector and run user code.

Of course the definition of "usable" work can be argued over but even a C64 released in the 80s will run your code in less then 10us

1ms is an enormous amount of time. I'm really curious why you would think otherwise

Because I understand electronics just enough to know that sending a usable signal in under a millisecond from cold is incredibly tough. That's barely enough time for voltages to stabilize in even quite high end systems.

Like I said link a microcontroller that can meet that. 'Usable work' can be as little as adding two half-precision floating point numbers together, and sending it can be any possible method.