If you choosed an average MRR for the roughing and average MRR for the finishing, would that give you a good rough estimate on the machine time?

I'm thinking like this:

Average MRR for roughing mulitplied by the volume removed by the roughing process + the average MMR for finishing multiplied by the volume removed by the finishing process = machining time.

An other question is what average MRR I should choose. Is it possible to take an average of the MRRs for many roughing processes on many different geometries and get a standard value that works? And the same for finishing of course. Do the average MRRs for roughing differ much between different geometries? And for finishing?

Could you give me a guess on a good MRR for roughing and a good MRR for finishing, that could work as a standard value for many different parts? We assume that we have the optimal machine with the optiaml tools, feeds and speeds for minimal tool wear.

Maybe I need to add the "lenght" of the smallest radius or something to get an better esitmate? And maybe need to have a standard for different standard for the MRRs when the geomtries are very complex or very simple?
And how do I best define the volume for the finining operation? Would it work to use the area of the finished part + 4 mm or something?