I'll throw my two cents worth in on this question. A lot depeds on the size of the marble and how badly the marble is hurt. I have completely reconditioned marbles in 1/2 hour (small, not hurt to badly) all the way up to 2 days (2 7/8" hand made 1/3 of the glass missing and this was before I started using a Diamond Arbor for the first step on these deeply hurt marbles.) Each person that reconditions marbles have their own methods (even though we use the same type of machine.) I now use a Diamond Arbor (last 5 years) as a fist step that saves me lots of time on the marbles that are deeply hurt. Most marbles that I do are done in three steps, but the deeply hurt ones are done in four steps. I never charge for the fourth step as it saves me tons of time.
If I just need to brighten up a marble I will go to the final polish step and that generally takes from 5 to 30 minutes. If it doesn't shine up enough to suit me I will take it through the pre-polish stage and than to the final polish . Now we are taking anywhere from 30 to 60 minutes.
So you can see it's rather hard for me to say just how long it takes for me to recondition a marble. I am speaking for myself only. ----Leroy----