Calibration pulse length depends on the plate scale (pixels per arc second) of your guide scope/camera.
When calibrating, PHD2 tries to move the mount by 25 pixels. The pulses are not in pixels but in seconds multiplied by guide rate. So, just try it once at 1000 milliseconds, and the look at how may steps it takes PHD2 to finish that 25 pixels. Scale it so that you complete 25 pixels in somewhere between 12 and 20 steps (better mounts with smaller errors will need fewer steps.
Remember that you need to calibrate autoguiding close to the celestial equator (or at leat no more than 30 degrees from the equator). There is a cosine relationship in spherical trigonometry, so that the calibration accuracy goes to pot when you calibrate closer to the poles.
Please read the PHD2 documentation if you have not already read through it.
Chen
