Hi Sharon
In that case I'd get the most from the sea by:
- Parking at Portovenere and either lunching there (we ate at a brilliant enoteca, but that was years ago and I'm not sure it's still there), or at Vernazza, depending on arrival time / boat times.
- Taking the ferry from Portovenere to Vernazza, which stops at Riomoggiore, Manarola, Vernazza (and also then Monterosso, which is a little larger/more functional than the other villages). That ferry trip is 1hr or just over, with no need to get off. That gets you to see 4 of the 5 villages from the sea, plus Portovenere as well. Nothing stopping you also adding Monterosso as well by taking the ferry all the way there.
Detailed schedule of boats in 2024 in the Cinque Terre, La Spezia, Portovenere and Levanto. Boat prices updated in 2024.
www.incinqueterre.com
- Lunch in Vernazza if timings suit - arguably it's the most picturesque of these picturesque villages and certainly the most picturesque harbour
Note also, that Corniglia isn't on the sea like the others. It's a hike (or shuttle bus) up to the village itself. I liked it's calm charm, but with the amount of travelling you'll have, I wouldn't overcomplicate it by trying to get up there, especially as the ferry doesn't stop there - simply enjoy the view of the beach, plus have a squint to see the village up on the hill.
So let's see how this stacks up for a possible rough schedule
6am leave Montepulciano
9am arrive Portovenere & park up, with plenty of contingency time, time to get the ferry ticket and to stroll around / grab a coffee and a croissant (also gives the option for a roadside stop)
11am ferry (assuming the ferry times stay the same) ariving at Vernazza 12:05
Lunch in Vernazza
2:40 or 3:30 ferry back to Portovenere, getting back at 3:40 or 4:30
Option to see a little more of Portovenere - perhaps having a light enoteca style snack meal, or head straight back to Montepulciano (c. 7-8pm if going straight back and having supper at 'home', or later if taking a further stroll around Portovenere)
This looks eminently more practical, very much being made so by your preference to only see most of the villages by boat. The moment you'd introduce a further stop, you'd probably add a minimum of 2 hours onto the schedule to see the place and make the next connection - and that would soon get to be the infeasible that I and Nico assumed.
So go for it - it's definitely doable on that basis.
Regards
Ian