It's interesting to have a read of all the different manuals as all of them are similar but may add a few additional words about backlash.
In the lathe manual it states backlash will prevent the effective operation of CV.
In the Mach3 software installation and configuration manual it says"Using it will generally disable the CV features at corners and Mach cannot fully honor
axis acceleration parameters when compensating for backlash and detune the stepper to avoid lost steps.
Then you have the Shuttle Accel comment from Hood posted ( it's not mentioned as such in the Using Mach3 Mill manual).
So each wording gives rise to a little different understanding to the user.
So responses to problems are use exact stop, adjust motor tuning and backlash settings. No exact answers when one considers all the differences in machines.
It falls on the user to find what works for them.
The Shuttle Wheel Accel is in seconds. How exactly is the" time" applied to the backlash "cycle"? Well I don't really know.

It's internal to Mach.

By observing the difference in how the motor reacts to different settings you will see that it affects the overall time it takes
for Mach to take up the backlash and at say a value of 5 you will find that over five seconds the handwheel / shaft will turn rather slowly.
At 0.005 sec its almost instantaneous. In the real slow setting, and say you jog a distance of .1" you will find there seems to be almost 3 distinct
motor responses in the cycle,....... a small rotation then deceleration...... then backlash taken up over a time...and then accel and move to finish the distance.
So to get of flavor of it you need to start slow, observe, listen to see what is happening over an operating range. Work your way up in settings.
RICH