you can't calculate running time from RCF. they are independent variables in one experiment. they are coupled when you want to for instance change one of them but not the possible final outcome. on beckman webpage you find calculation tools for their rotors. ask them for the catalogue (i guess they can send a pdf) for the formulas.
can't answer the second part of your question. sorry.
I advise you to contact Dr. Helmut Cölfen at the Max-Planck Institute of Colloids and Interfaces - Golm - Potsdam - Germany (hope he is still there), he is a well skilled with ultracentrifuge and may help you for sure. Regards