The area of Parco Nazionale delle Cinque Terre is relatively small and yet, one day trip isn't enough even to get an idea about it, especially if your agent has "run and gun" idea of visiting the park.
The walking trail in between Riomaggiore and Monterosso al Mare is 9km long and it takes about 5 hours. The longest single distance is 4km and it's between Vernazza and Corniglia. The distance is, however, absolutelly irrelevant in terms of duration, all depend on individual choice.
The best way to get around Vernazza and the Cinque Terre is by foot.
Walking along the cliffs between villages is a fantastic experience and the views are spectacular.
You don't need proper hiking shoes, but sturdy foot wear is a must. Leave the stilettos at home!!
We saw lots of people walking with poles, which may have made some of the steeper climbs a little easier - harder to juggle the camera though!!
We stayed in Portovenere the first night in Italy, a difficult place to get to from Genoa airport, it took almost 4 hrs, using a bus from Genoa airport to the train station, a train to La Spezia and then a bus from there to Portovenere. Although, due to markets on in La Spezia we caught the bus going in the wrong direction, so a 20 min trip turned into 1hr :-)
We decided to get an early start as we had planned (using the Lonely Planet "Walking in Italy" book as our guide) to walk from Portovenere to Vernazza on the first day, then on the 3rd day walk from Vernazza to Monterosso.
Unfortunatly the Lonely planet let us down, it said that the Portovenere to Vernazza trip should take around 6 hrs and that the terrain was of easy grade. We have done a lot of rambling in England and Scotland, but did not find the first half of this trip to be easy, more like moderate with some narrow paths and some scrambling along rocks. There was also a fair amount of altitude climbed (for the non-alpine walker). The heat was really taking it out of us - at 35 degrees and no breeze, but the views from the tops of the cliffs were spectacular. It took us 6 hrs to get to Riomaggiore. We went into the tourist office and they confirmed that 6hrs was the norm for that stretch of the trip. The final stretch was another 4 hrs! We decided at this point to take the train from Riomaggiore to Vernazza, and do the coastal part of the walk the next day. So, after our experience my tips would be, catch the ferry from Portovenere to Riomaggiore then do the coatal walk or break the trip into 3 days of walking, especially in the hotter months.
Even if you arrive to vernazza by car, you'll have to park VERY FAR from the city, and take a long walk from there down to the town. THere are several parking lots, and on the distance from the town it depends which is the price. Only the very privileged inhabitants of Vernazza can use the parking place right in front of the town. Others have to walk. But don't worry, it's a nice walk! :)
There are no busy intersections, no traffic lights, withing the town of Vernazza. A good pair of comfortable shoes is all that you need to enjoy this romantic place.