Its been there for a long time, almost since the beginning of Mach3 but there will still be the delay that, the laser guys see, even when set to zero. I am not sure but I think the delay may be because when you call a M3/M4/M5 Mach will look at the macro so you get a slight delay, this is not a problem for machine tool spindles but for lasers the small delay is a problem.
M11/M10 was I believe the way Art made to get round this short delay issue.
Hood