I don’t know the answer re. either question. I noticed this behavior some time ago when I was first seeking a solution to LB and plasma process. Yet another question is: why does ‘cut through’ have to be enabled in order to get the ‘start pause time’ (aka pierce delay) to occur after the M3 command ? without ‘cut through’, the delay is before the M3 command and I’m not understanding what purpose that serves other than perhaps XY stoppage/location mechanical dampening. LB support will have to answer.
In my use case of LB and plasma process, I use GRBL-M3 device mode as you do, but I don’t use the ‘start pause time’ attribute, nor do I use ‘cut through’. Rather, I post-process the LB laser g-code replacing M3 and M5 with my own code blocks. In the case of M3, to perform per-cut torch touch-off with job surface giving a precise (+/-.1mm) Initial Torch Height and Pierce Height, as well as including a Pierce Delay and a torch (Z) ramp down on the LB line lead-in; and in the case of M5 to perform a torch off delay and a torch (Z) safe retract before having LB move to next cut.
The post processor is a VIM editor script. download it from this thread.
I hope this helps, happy to field questions as needed.
Lou