I’m not sure what this formula is representing here. The ‘1000’ value in the $30 setting is just the maximum value that GRBL expects to see, and will produce 100% output on the Spindle PWM pin. Older versions of GRBL only have 8 bit PWM, so they use 255 as the maximum. Newer GRBL defaults to 1000, so that’s LightBurn’s default as well.
If you use the “Find My Laser” tool in LightBurn to set up your machine, it queries the controller to find the correct value and sets it for you. As long as the number is at least 255 your should get good power control, and the two numbers have to match, but you would see no difference in speed of output between using 255, 1000, or 5000. It’s just a mostly meaningless number.
To get the simulation times more accurate, look at the machine settings for acceleration and max speed ($110, $111, $120, $121) and copy those numbers into the speed and acceleration settings Rick showed above. Rapid speed is the same as Max speed. Cut and engrave accelerations will use the same acceleration values.