I have taken that trip a few times--with my family a few years ago. It's about 2 hours as I recall (a long 2 hours on the last trip, as it was July and we had an unventilated relic of a train) and the train stations in both places are very convenient for walking around town (my youngest child was 4 and we managed without a problem).

There is more to see in Venice, but the food in Bologna is tops. I am envious.

JoAnne in rainy northern California