In Bruges on April 25, 2019 from 7 AM - 6 PM

Bruges is a wonderful walking town so I would recommend taking one of Rich Steve's walking tours and stop and have a delicious lunch complete with frites and a brew or two!! We took a bike tour of Bruges that included getting out of town along the canals complete with windmills and beautiful countryside but your time may be a little too tight for that.

This (Rick's) website has good suggestions on prioritizing the many things to do in Brugge/Bruges.

There's lots to see in Bruges, and best to do some reading up in advance to choose what appeals and get a handle on the town's layout. Their tourist board has a nice website that will be helpful!

https://www.visitbruges.be/en

Crowds will be densest around the Markt and Burg and some of the more well-known attractions, such as Church of Our Lady (Onze-Lieve-Vrouwekerk).

Also scan the forums for threads regarding similar questions for things to do, such as this one:

https://community.ricksteves.com/travel-forum/belgium/brugge-for-whole-day

Skip Choco Story, Frietmuseum (although DO buy and gobble up some frites from a street shop!) and Historium.

Bruges is s great town to walk and browse.
Be sure to see the Church of Our Lady.
Enjoy lunch in the Square - can recommend Panier d'Or, although there are lots of cafes.
Lots of chocolate shops, we bought from several including the Chocolate Line
Have fun!

I am guessing you are on a sea-going cruise. Brugge is not on the coast, it is inland. The reason Brugge is so well preserved is that it used to have sea access, but it silted up, transforming Brugge from stinking rich to being too poor to re-build out-of-date buildings.

The modern port is Zeebrugge (=Brugge-on-sea), and is as you say ~20Km from Brugge. Definitely go to Brugge, Zeebrugge is a harbour town, nothing to see.

There is a train line from to Brugge, but I understand the boats dock in the harbour, not within easy reach of the station.
If your cruise company offers a bus to and from Brugge, I would take that, as it would be the most convenient option, and would be direct from the ship.

Lots to see in Brugge, with not even a full day, you can fill it just walking around town. Lots of good restaurants serving local dishes.

Your concern will not be if going, but how going to Bruges. Depending the cruise a bus wil bring you to there, or the station of nearby Blankenberge for taking the train to Bruges or just to the terminal exit, in that case you have to arrange your own transport. For the latter you can take a taxi, sets you back €55 or the tram to the train station in Blankenberge. For the tram you have to walk some 10 minutes along the main road to the stop near the church, a landmark easy to see when docking. The driver sells the tickets, €3 each, are valuable for 1 hour, so if you arrive within that time at the train station in Bruges you can take the bus there to the centre -Market Square (Markt)- with no extra charges.

The bus and tram are serviced by “De Lijn”, the train by SNCB/NMBS you need to buy seperate tickets at the train station.

But first contact your travel agent what is included. There is now a new cruise terminal building in Zeebrugge and think according planning operational now. https://www.portofzeebrugge.be/en/cruise/terminal-facilities

As Will suggests, check with your cruise line or travel agent.
If you are 12 miles away from Bruges, it will take less than 30 minutes to get there. That means you will be there well ahead of a lot of crowds and likely before shops open. You will be able to cover Bruges even on foot without any problem; they may even drop you off close to the middle of town (another question to ask)

These itineraries are set well ahead of time and the cruise line can tell you how you will get to Bruges, the best way to get around and return back to your motor coach to return to the ship.

The ship will have a cruise director who is well-versed in these excursions.

We did a river cruise this past April in the Netherlands; these cruise lines are very customer oriented and should provide you with all you answers.

Have fun planning!