If you only have a day in Belgium, and it is spent drinking Belgian beer, (which I love but can be quite strong) then that is going to be pretty rough!
Write it all down, including travel time.

You can drink all the Belgian beer you want in Paris too. No need to go to Brussels or Brugge or anywhere for that. The only Belgian city that has a good bar culture is Gent.

http://www.beeradvocate.com/beer/pro.../view=beerfly/

Right outside Gare du Nord!