I don’t know if you read my G00/G01 post, but the jerk is surprisingly not the derivative of the acceleration, it’s a speed, and below that value, the software doesn’t account for the acceleration when determining the speed to drive at. At the corners, it normally would be slowing down, and speeding up, limited by the acceleration. Any speed below jerk, doesn’t get that filtering. So if you set your jerk to 900 mm/min (I can’t remember the units on the jerk config value), then the software would immediately start pushing the stepper to 900 mm/min. Whether the stepper gets there or not, is going to depend on hardware things like the driver current setting, and the mass of what it’s moving. If it can’t go that fast, you will get skipped steps.
If jerk was 450 mm/min, then it would immediately go half speed, and ramp up to 900 mm/min based on the accel value.
So if you want immediate speed, with no ramping at all, then set the jerk up higher. But if you get any skipped steps, you’re screwed. If you want to reduce the amount of time it goes from low speed to max speed, you can increase the accel, but it will always be ramping up anywhere above the jerk setpoint.
I doubt there’s any solution w.r.t. predicting the speed it will be moving, and adjusting the power output of the laser. I also don’t know if it might make sense to plan to overshoot the corner, but turn the laser off. That would probably be worse problems…