We have been on the same cruise that he is going on. Considered doing exactly the same but decided to do it the following day from Livorno (which is an overnight stay).
His day is actually 7:00am to 4:30pm (when he must be back on board. From the ship (via tender) to Portofino, then local bus to Santa Margherita will take probably an hour. He should figue 1½ hours coming back to account for 'waiting for the bus'. Train from Santa Margherita to Riomaggiore (southern most village) will take at least an hour. Coming back to Santa Margherita he should plan on 1½ hours to account for 'waiting for the train'.
Realistically speaking he should have 4½-5 hours in CT. He needs to spend a lot of time getting very familiar with the train schedule to/from Cinque Terre from Santa Margherita, as well as the schedules between all five villages. To go without doing this is asking for trouble. This type of trip requires a lot of detailed plannning, with at least 1 (if not 2) back-up plans.
Radiance of the Seas - Nov 2006
Legend of the Seas - Jun 2007
Costa Fortuna - Mar 2008
Legend of the Seas - Oct 2008
Celebrity Constellation - July 2009
MSC Orchestra - Jan 2009
Navigator of the Seas - March 2009
MSC Poesia - November 2009
Jewel of the Seas - June 2010