Welcome to the forum! We’re here to help!
Yes, the computation can take a while. If your machine isn’t a 4GB plus RAM machine with two or more screaming cores you will have to wait… or play with the amount of data emitted. The more data MeshCAM has to work on, the better job it can do with the machining.
In general, your CAD should spit out as fine an STL mesh as it can and the roughing tolerance should be 0.0001" (or 0.0025 mm).
Could you please post a screen shot of the parameters you’re using for the machining? That would help us understand what’s going on. Could you also please make sure we can see the scale of the cube (1 inch, 25 mm)?
One thing that may help is to enable the use of G02/G03 (G-code for circles). This is currently commented out of the MeshCAM post processor for the Nomad. This is an optimization… we can go there once we figure out what’s going on.