Ghent

Since you have so little time in Ghent, I'd do the canal tour in Bruges. Over the years I've done canal boat tours in both and to me Bruges is prettier.

For Sint Baaf and the Altarpiece, be sure to go to the official site and get tickets ahead of time. Do the Augmented Reality program which starts in the crypt and gives the history of the altarpiece, then you go upstairs to the chapel where the Adoration of the Mystic Lamb is installed. I was there last April and several of the days I was there were completely sold out. They do limit the number of people but once you are in you can stay as long as you like in the chapel area.

https://www.sintbaafskathedraal.be/

Since you mention Evening, be sure to download the sunrise/sunset time somewhere on your itinerary for reference. Lots of things will be closed in the evening. But Ghent is a nice (if smaller area than Bruges) walking town, and (finding a good restaurant aside) you don't need to go indoors to enjoy the walking view of the town. Canal boat tour is forgettable. I had informal lunch there but not dinner. There is a music school so maybe student concerts if on your visit day?

There is a nice art museum (nothing to do with St. Bavo's) if you like indoor art. Note that the train stops almost a mile from the old town, so you'll have a bus ride or a 15-minute walk. Bus ticket machine and stop right outside the train station. Same transit card (if you already have one) as Bruges.

I don't have a problem with seeing Ghent in a half-day, but it sounds like your trip is tightly scheduled. I personally prefer Antwerp to Ghent or Bruges, but that is a matter of personal opinion. One reason I mention it is that in Antwerp, Rubenshuis (if open, may have works in progress), Rockoxhuis, and the Maagdenhuis are nice interior architecture and decoration opportunities. (Not much "art" on the walls, I'm talking about older buildings you said your husband likes.) There are also some very fine churches in Antwerp. There is also a major (100 +-) townhouse development from 1900 with a variety of architectural styles (exterior views only), called the Cogels Osy Lei. There are some notable art deco and art nouveau exteriors in Antwerp.

I felt that most of the main sights in Ghent were in a fairly small area so you should be able to walk around and see everything in the time you have. You’ll see St. Michaels bridge from the Graslei and Korenlei area, and the guild hall is nearby. We just walked by the belfry. One place I enjoyed was the Werregarenstraat. It’s an alley with bright paintings/graffiti on the walls. We took a canal ride in Bruges, so skipped it in Ghent.

Thank you to all 3 of you for the very useful information! I still have time to move some things around for our time in Belgium if I need to. I have been planning since August of last year. Right now I roughly planned on a full day and a half to be in Bruges including an architecture walking tour I scheduled there. I plan on a half day in Ghent and a full day in Brussels. Then on our way to Delft in the Netherlands I plan to stop in Antwerp for a half day. I will definitely get tickets ahead of time now for St. Bavo's Catherdral. We will do a canal tour in Bruge, if we have time for one in Belgium. I will try to get to the Werregarenstraat to see the paintings/graffiti. And we will try to see the townhouse development mentioned in Antwerp.

I have done boat rides in both towns - in Bruges there were (pre-covid) greater crowds, more boats, a scenic ride the whole way round, different joining points. In Ghent there were no crowds (just the two of us on the boat with the driver/guide), a less interesting route, less interesting buildings on the chosen route, and only one choice of route/boat.

I'd repeat the Bruges one if the crowds weren't a bother if I were taking somebody, I would miss the Ghent one (and I love Ghent).

In Antwerp, architecturally I enjoyed the art nouveau Het Bootje. Believe it currently serves as the Chilean consulate. It is about a mile walk from the cathedral and Nello & Patrasche statue at Plaatsnijdersstraat 1 and the corner of Schildersstraat. Another quick stop was to see the all wooden escalator at the Sint Anna tunnel. It’s an interesting curiosity since very few remain.

In Ghent you can do the following walking tour starting from the Korenlei. From there north along Jan Breydelstraat to Sint-Veerleplein and Gravensteen. Further you can cross the “Geldmunt”street or make a detour via Gewad, Sint-Widostraat and Lievestraat to for instance the alley next to the Kunsthal Gent for a walk through “Het Patershol” to the Vrijdagsmarkt (Fridays Market, still today the place for the weekly market). After a little detour to “Antiek-depot market15” (vintage shop) in the Baudelostraat continue further to “Bij Sint-Jacobs” , best time is Friday, Saturday or Sunday during the morning for the weekly fleamarket.

From there along Serpentstraat to Werregarenstraat for the grafitti. Via Hoogpoort and alley Biezekapelstraat to Sint-Baafskathedraal (Saint Bavo Cathedral). On the way to Korenmarkt and Groentenmarkt pass along the Belfort (Belfry, every day open to climb) and Sint-Niklaaskerk, a late gothic church well worth to see inside. Finally from Groentenmarkt to Graslei / Korenlei to complete the walking tour.

After sunset this part of Ghent is beautifully illuminated, you can take the latest tram / train back to Bruges.

The TI is in the Oude Vismijn (old fish market) at Sint-Veerleplein and a good place for a drink and a nice view of the Leie river.

Above the entrance of the NTGent theatre there is a little cafe terrace with a nice view of the square between the Belfry and Sint-Baafskathedraal. With a bit of luck there is table free for enjoying the view.