(1a) Thank you for the typo correction.
(1b) It means that moves shorter than 3 ms may not be reliable. Keep your moves at least 3 ms long.
(2) You say “But in most cases the axidraw “crack” and don’t execute the command correctly.” I’m not sure what you’re saying — if something is breaking, please contact us via e-mail and we can work with you on the repair. If the EBB is not executing a command correctly, please let me know exactly what command you are executing, and in which way the behavior was not as expected.
The EBB firmware gives an upper limit for how fast it can generate steps. That is not the same thing as saying that the machine can physically move at the maximum step rate that the firmware can produce. The maximum physical movement speed (as in steps per second) depends on the mechanics of the machine, the resolution selected with the EM command, and how fast or gently you have accelerated.