Venice side-trips - Verona & Padua in a day?

I think it's completely doable. There's a 07:50 Frecciabianca 9708 that would get you to Verona Porta Nuova in 1 hr 10 mins (arrive at 09:10) for €19.00. A mid-afternoon train would get you from Verona to Padua in only 42 mins. With the long summer daylight hours you could stay into the evening, have dinner, and then catch a 30-min. regionale as late as you fancy back to Venice for a Midnight stroll to your hotel. May I join you? (kidding!!) Sounds like a great day. (My train query used a dummy date; your results for your date may vary.)

Doable, yes in the sense that you'll be able to see a few of the major sights in each location. Advisable? That depends on how much sightseeing you like to cram into one day. Personally I like to take a break mid-afternoon. As I often say, there is no one-size-fits-all approach to travel.

I think there's so much in Verona, it would be a shame not to spend a whole day. Look at the Verona Card website to learn what the city offers. Verona is one of my favorite places.

Thanks for the responses! I, for one, like to plan every day to be full and relish getting everything done, but I will be with a big group so it won't be all up to me. :) Chani, anything in Verona you enjoy particularly? Would appreciate any tips! :)

My two favorites are the Arena in the afternoon sun. Be sure to check at the entrance for the hours. I missed seeing it on my first visit, because they closed early to set up for a concert. Even the TI at the train station didn't know about it. and San Zeno Maggiore Church and the walk back along the river. The Lamberti Tower has a nice view. There's an elevator. I really liked the Castelvecchio Museum, but I like museums more than most. You do get to see a lot of the castle too. But you can see the outer walls and the courtyard without entering the museum. Juliet's House was pretty crowded and the whole balcony thing is too corny. It is a rich man's home from the 16th century, so it's sort of interesting for that. I was disappointed with the Roman Theatre.

You haven't indicated what your interests are, so I'll just point out what we thought were the highlights of Padova. First and foremost, IMO, is the Scrovegni Chapel, with Giiotto's fresco cycle (need reservation). The baptistery also houses a remarkable set of frescoes by Menabuoi. Other noteworthy sights include Palazzo della Ragione, Caffe Pedrocchi, and the Basilica of St. Anthony. My recollection is that most of the sights are close to each other and to the train station; but the basilica is a bit further away. Even with a car, we did walk to everything; however, since driving around an old Italian city is counterproductive.
By the way, you might be interested in the cruises on the Brenta Canal. They go from Venice to Padova and vice versa on alternate days, stopping at some Palladian villas along the way. I think Palladian architecture is also a don't-miss for the Veneto region. They have full and half days tours. It's been 6 or 7 years since we took the cruise, so my memory is a little fuzzy; but I believe there are two companies which do them. You could google "Brenta Canal cruise" to get more info.

Verona is spectacular in almost every way! Beautiful, old city center that is very little changed for hundreds of years.
If you are fan, or just want a true Italian opera experience, go see the opera in the Roman colleseum that's in town. During the summer they stage a series of operas that are on a scale not done here in the US. You sit on the ancient stones under the stars and experience THE BEST opera there is. I saw La Boheme there a number of years back and won't go see that opera again because I believe it couldn't be done any better! It's a very Italian crowd as well...before and during intermissions there are guys going around selling "Coca, bierra, Fanta!!" at the top of their lungs and people shushing each other if they so much as whisper during the performance...it's a once-in-a-lifetime sort of experience!