Upgrading a PDB from 12.1.to 12.2 using unplug/plug

Hi,

   My customer is investigating the possibility of upgrading his PDBs from 12.1.0.2 to 12.2.0.1 by creating a new CDB at 12.2.0.1, then unplugging the PDBs from the 12.1.0.2 CDB and plugging them into the 12.2.0.1 CDB. I see from MOS note 2171026.1 that 'catupgrd.sql' then has to be run (perhaps by means of 'catctl.pl' or 'dbupgrade). I imagine this will be a very short activity, as the only components to be affected would be those parts of the data dictionary which are part of the PDB. What are the factors which determine how long this will take to run?

   I would be grateful for any thoughts which you may have.