Bogna-oriveto-rome

Hard to say. Ravenna is worth an overnight stay because the streets in the city center are wonderful to wander around. I have been there many times and spend the night when I bring someone there. Orvieto is one of our favorite towns and is worth spending the night because all the busloads of people will have left. I live half the year not far from Bologna and I chose the town because I like Bologna but for visiting as a tourist.... Ravenna and Orvieto would be my choices. You do have quite a few days though... Bologna is a better hub than Ravenna to reach other towns. I wouldn't miss the mosaics and charm of Ravenna.

I think this distribution is pretty good. Assuming you're really okay without a day in Rome you have one extra day to play with but I think 2 nights each in Ravenna and Orvieto is good timing. It's one full day and two parts of day with varying amounts of time. If you wanted to add another to either of these Ravenna is bigger.

You could add the "extra" Rome day to Bologna since it has many interesting day trips from there: Modena, Parma, Ferrara, Florence and even Verona at a stretch just as a start. If after two days you feel like you've seen Bologna there are plenty of interesting places to spend the day seeing. I'm assuming you've chosen Bologna as your large base for good reasons. Florence could easily eat 4 nights even without a day trip to Siena.

I think your plan is fine, but it's your time and you trip and it can be adjusted.

My $.02,
=Tod

I don't see how you could manage to reduce the number of stays unless you forgo seeing one of them. How many nights do you have? When you say "days", do you mean full days or partial days? What time is your flight? I have gone from Orvieto by train to FCO, but I had a 10 pm flight.