Greetings,
I happen to know Engineers whom have worked on the FMS2, the info I have released are genuine, and some are not in the FCOM, however 1 minutes time difference at 20 nm is too much (it will mean that the distance has at least an extra 8 nm
so the ground speed difference would be huge, considering the proximity of the point)
as far as I am concerned I have never witnessed such difference (Which doesnot mean that it doesnot happen) and if I had, I would have logged it and send it to Airbus.
Now for the record the FMP Flight Management Processor performes computation (Smiths side of the FMS) and the IDP Interface and Display Processor (THALES side) displays the results on the ND and the MCDU.