Acceleration is velocity over time, so in Mach velocity is in Units per minute and acceleration is units per second per second.

So first thing you need to do for the calculation is change the set velocity from units per minute to units per second.

So for your example 1000 units per minute it would be 1000/60 = 16.666666667 units per second.

Ok so now we know the velocity in Units per second we can work out how long it will take to get there with the acceleration you have set in Mach.

So you say you have 1000 units/s/s acceleration. That means it will get to a velocity of 1000 units per second in 1 second.

That is way faster than your velocity however as your velocity is 1000 upm so only 16.66667 units per second.

So to get the time it will take to get to your velocity you can work it out a few ways, one is to just simply divide your units per second velocity by the acceleration, so 16.66666667/1000 = 0.016666666667 seconds to get to max velocity.

You mention RPM however so I am not sure exactly what you are meaning. Obviously the rpm is the max value in the drive but what do you actually have in Mach? If you have 1000 set for the Velocity then that will not be 1000rpm at the motor unless your ballscrew was 1mm pitch which is unlikely. So say it is 5mm pitch then that would mean for 1 rev of the motor you would move 5mm so the velocity in mach for a motor rpm of 1000 would be 5000mm/min.

If that is the case then the time to get to max velocity would be

5000/60 = 0.08333333333333 seconds.

Regarding the value for accel set in the drive, I do not think it will matter at all. I think that setting will be used only when there is an internal drive command such as indexing or internal speed command etc.

As you are controlling the drive via the analogue inputs (step/dir would be the same) then you are also controlling the velocity via that method and thus the setting in the drive is irrelevant.