Don't know if I can help with this but I'll try.
These input boxes aren't particularly well labelled or documented but they are covered albeit briefly in Art's video "Installation and Basic Configuration". In it he states that these values are ADDITIONS to Mach's standard step and direction PULSE WIDTHS.
He defines Mach's standard behaviour as being "approximately" 1 to 2 uSec for both. I assume (but may be wrong) that it's Mach's signal jitter that prevents him from being more accurate.
The Step pulse box:
Using a gecko 202 (other excellent drives are available) as an example, the manual says (for the step signal):
"The minimum logic “0” time is 0.5 uSec .... Microstepping occurs on the falling edge of the step input"
So the "approximate" 1 to 2 uSec that Mach delivers is MORE than adaquate, so with this particular drive there is zero point in extending it. You can of course extend it to anything you like - it will make no difference whatsoever except if you go reaaaaaaaaally long (and why would you?) and particularly at a high Kernel rate you will ultimately affect your potential max step rate!
There has been mention of the Max pulse width. The reason there is no MAXIMUM for pulse width is because the minimum is all that matters for correct switching of the electronics. i.e. with the example gecko drive the step signal falls and as long as it's kept low for the minimum 0.5 uSec the electronics will "do their thing".
Onto the The Dir "Pulse" box:
I quoted Art above as saying that this value (like the step pulse) is an ADDITION to the Dir PULSE WIDTH. This in my view can not be taken at face value and needs a bit more thought. The Dir signal (at least for the gecko and for every other drive I have ever seen and/or used) is treated more as a STATE than a PULSE. i.e the Dir signal does not LATCH the drive on a falling or rising edge, rather, it's STATE either high or low is "read" by the drive WHEN it receives a step pulse. The issue of course becomes particularly interesting when the Dir signal CHANGES and this along with Art's description are the clues to what I think this value ACTUALLY means. Here's another quote from the gecko 202 drive manual:
"Direction Setup: 1uS min (20uS min hold time after Step edge)"
Now of course this tells us that the minimum PULSE WIDTH of the dir signal is 20 uSec but I don't think this is what this box value refers to. I think it's the setup time of a CHANGING dir signal of at least 1 uSec BEFORE the falling edge of the next step signal. Therfore Mach's default of the "approximate 1 to 2 uSec" is again absolutely fine (for a gecko at least). The reason I think this is because Art states that this value should be changed if you have the problem of missing a step on a direction CHANGE (yes that old chestnut).
FWIW the direction hold time would only be of issue if your application wanted to change direction more than 50000 times a sec! Hmmmm - cutting microscopic saw teeth perhaps!
So as summary: Check your drive's tech spec and set accordingly by ADDING to the default 1 to 2 uSec if required, or if you prefer, leave both values at 0 unless you have problems.
Cheers
Ian